* Add arrowhead support

As described in TODO, dotparser.js does not support 'arrowhead'
attribubte of edge.
This update is for adding 'dot' and 'tee'(bar) styles.

* Add example for arrow styles

* Add box arrowhead

To support box arrowhead of graphviz, add Box endpoint class in
EndPoints.js and box attribute in dotparser.js.

* Add diamond arrowhead

To support diamond arrowhead of graphviz, add Diamond endpoint
class in EndPoints.js and diamond attribute in dotparser.js.

* Add crow arrowhead

To support crow arrowhead of graphviz, add Crow endpoint
class in EndPoints.js and crow attribute in dotparser.js.

* Add normal arrowhead

To support normal arrowhead of graphviz, add Triangle endpoint
class in EndPoints.js and normal attribute in dotparser.js.

* Add curve arrowhead

To support curve arrowhead of graphviz, add Curve endpoint
class in EndPoints.js and curve attribute in dotparser.js.

* Add inverted curve arrowhead

To support inverted curve arrowhead of graphviz, add InvertedCurve
endpoint class in EndPoints.js and icurve attribute in
dotparser.js.

* Add vee arrowhead

To support vee arrowhead of graphviz, add Vee endpoint class in
EndPoints.js and vee attribute in dotparser.js.

* Add arrowhead examples

* Fix bug for accessing null attribute

In createEdge(), accessing 'attr' causes an error if the edge has no
attribute and the value is null.
This update fixes bug for accessing null 'attr'.

* Update description for arrows.to.type option

Add followingn options for 'arrows.to.type'.

* box
* crow
* curve
* diamond
* inv_curve
* triangle
* inv_triangle
* vee

* Update edgeStyle example for arrow types

Add arrow types for the example.

'box', 'crow', 'curve', 'inv_curve', 'diamond', 'triangle',
'inv_triangle', 'vee'

* Add support for `icon` option to ShapeBase

* Add test/example for new ShapeBase `icon` option

* Update docs for new `icon` ShapeBase option

* Docs : fixes and enhancements for the documentation template.

This is an evolutionary update for the `jsdoc` document generation.

- Added functionality to retrieval of data comments
- Added partial for generating documentation in the method tables.
- Moved commenting to source for `Network#clusterOutliers`. This was used as a case example.

- Adjustment to CSS to get the decription text margins same as original
- Added step to generate documentation to release checklist
- Fixed some commenting which `jsdoc` couldn't handle

* Fixes for linting

* background docs
* edge background
* Update edges.html
* Update EdgeBase.js

* Moved navbar elements in all html documentation files to partial

This consolidates the common menu elements in all documentation files to a partial.

* Moved test-exclamation mark

* Added partial, tested with some pages

* Docs: Moved end block in all html documentation files to partiel

This rcConsolidatersd common footer in all documentation files to a partial.

I'm hoping this serves as an example for others to isolate more common blocks (the menu would be the perfect candidate). It's straightforward work.

* Add template for document generation with 'jsdoc'.

In essence, it defines the subdirectory `docs` as a `jsdoc` template. Benefits:

- allows the usage of partials, in order to DRY common parts of the html files.
- makes available the jsdoc-comments, for addition into the documentation.
- enables extraction of data from the source code. For example, the list of edge endpoints `['arrow', 'bar', 'circle']` can now be extracted from the source and inserted into the documentation on generation.

In this initial version, the only file that has been changed is `docs/data/dataset.html`.
In here, partials have been added to illustrate how common page elements can be DRY'd.

The template has been set up in such a way, that resource files will be copied and that html files can pass through unchanged if no special template tags (`<?js...?>`) are used. This allows for a gradual transition of the html files to templates.

**Usage:**  `gulp docs`

- The result files are placed in subdirectory `gen/docs/`.

**NOTE:** The release procedure will have to be adjusted by adding this gulp command.
The docs-files will then have to be taken from `gen/docs`.

* Edits to docs/README

* Adjusted layout of README.md

* Further edits to README.md

* Removed pre tags again in  README.md - don't work in code block

* Linted the gulpfile

* Added proof of concept for docs generation from source

Fixes #3468.

Rather than changing the code, this resolves the issue by adjusting the documentation for event `stabilized`.

* Small refactoring in Label._drawBackground()

* Added size calculation to Label, basic framework for detecting click on label.

* First fully working version of label click.

* Put in extra checks, refactored visibility of labels for more general usage.

* Final fixes to code; added to example and in docs

* Adressed review comments

* Add next attempt to fix Travis unit test bug

* Addressed review issues

* Network: Adjust documentation for arrows.middle.scaleFactor

Addendum to #3474.

Updated the documentation, so that users can know about flipping the middle arrow with a negative scale factor.

* Adjusted text for review

* Add endpoint 'bar' to Network

Fixes #3412

- Adds class `Bar` and handling to `EndPoints.js`
- Adjusted `options.js` for endpoint, minor code changes
- Added to example `network/edgeTypes/arrowTypes`.
- Added to edges documentation

* Grumbl fix travis unit test yet again. Go die already!

* added hexagon shape to the node.

* Updated function for hexagon shape.js

* Modifid the shape login for hexagon

* Remove this.translate from the Shape.js for hexagon

* updated hexagon draw logic

* Fixed code review comments and update the branch

* Updated changes in test.js

* Fixes Issue #3316 - Updates network documentation to account for edge-case of how clusterByConnection uses the joinCondition callback

* Move the text 'clusterByConnection will pass ... callback.' to under 'Optional for all but the cluster method'.
Make it clear that clusterByConnection is the only one that uses the second call.
Instead of bold, make it a distinct paragraph.

* First interim commit

* Fixes during testing

* Allow multiple edges to be hidden by a clustered edge.

Fix for #3245.

This fix adjusts the clustering edges so that theyi can refer to multiple edges instead of just one.

This API method is now insufficient, since multiple base edges can be returned.

- Added replacing method `clustering.getBaseEdges()`
- Adjusted example `changingClusteredEdgeNodes` for the new method. This is the *only* place where `getBaseEdge()` was used
- Adjusted documentation for new method and deprecation old method.

Method `getbaseEdge()` should now be considered `deprecated`, and in due time should be removed.

* Edits of method name in example

* Edits of method name in example

* adjusted deprecation method getBaseEdge() in docs

* Adjusted deprecation method for getBaseEdge() in docs

* Protect Network from zero and negative mass values

Fix for #3133

Option-field 'node.mass` must be >= 0.
Checks have been added at the nodes level, for both nodes-global and nodes specific options.
In addition, an internal check has been added for `NodeHandler.defaultOptions`.

The documentation has been adjusted for this change.

* Fix whitespace

* Prevent crashes from invalid id's in `Clustering.findNode()`

Fix for #3163

- Added safeguards in said method, to prevent exceptions happening when invalid id's are passed in.
- Adjusted documentation for said method
- Added notes to flag unused methods in `Clustering.js`

* Removed incorrect NOTE-comments from methods that are indeed used

* Added param 'direction' to Network.getConnectedNodes()

* Redo commit - Network.js does not need to change

* fix #2613 with if statement, and null for pointer value rather than referencing it when undefined

* removed if statement, since not needed, and updated documentation to note the null pointer property in certain conditions.

* element characteristic changes
* assume edge color inheritance is correct before choosing
* Adjust nodes’ chosen’s boolean -> bool
* Need to get user-reset size
* make example edges thicker for more noticeable shadow
* preemptive ES6 fix (see #2500/#2501)
* documentation for the feature that was previously overwritten

* Multifont node and edge labels
* adjust documentation
* rework mod-font property inheritance
* Node max/min widths, min heights; Edge max widths
* Accumulate sizes correctly for unconstrained multipoint labels
* handle font.multi when groupOptions.font is not declared
* propagate label fonts on changes, not just creation
* Allow top-level constraint numbers
* accumulate width and empty lines appropriately

* add pointer position to zoom event
* Update docs with zoom api

* { manipulation: { editEdge: { editWithoutDrag: function } } } edits an edge without dragging.
* An example of editing network edges without dragging, enabling label creation / change

Thanks @federicoco for providing the translation!

* Removed restriction to allow clusters of a single node; Default functionality remains the same;  Also added new example
* Add documentation for allowSingleNodeCluster, and removed excessive cluster() calls in example.
* Changed documentation as per request.

* Added getBaseEdge, getClusteredEdges updateEdge and updateClusteredNode to allow option changes of the clustered edges as they are no longer the original base Edge

changing edge color is a good example.
i.e network.clustering.updateEdge(originalEdge.id, {color : '#aa0000'});
will now update all edges including the ones that were created when clustering.

Also when clicking on a clustered edge the event returns the clustered Edge id, which doesn't mean a lot.
This can be now converted back into the original edge with
network.clustering.getBaseEdge(clusteredEdge.id)

Similar with updateClusteredNode
This new method allows the options to be changed on a clustered Node.

i.e clicking on a clustered node gives its clustered node id.
Want to change the clustered image to a star then do this
 network.clustering.updateClusteredNode(clusteredNodeId, {shape : 'star'});

* Updated docs with getClusteredEdge, getBaseEdge, updateEdge and updateClusteredNode

Also added method subsections into contents

* Added better error handling to updateEdge and updateClusteredNodes

corrected errors spotted by @mojoaxel

* Added example html demonstrating getBaseEdge, getClusteredEdges updateEdge and updateClusteredNode

* Added getBaseEdge, getClusteredEdges updateEdge and updateClusteredNode to allow option changes of the clustered edges as they are no longer the original base Edge

changing edge color is a good example.
i.e network.clustering.updateEdge(originalEdge.id, {color : '#aa0000'});
will now update all edges including the ones that were created when clustering.

Also when clicking on a clustered edge the event returns the clustered Edge id, which doesn't mean a lot.
This can be now converted back into the original edge with
network.clustering.getBaseEdge(clusteredEdge.id)

Similar with updateClusteredNode
This new method allows the options to be changed on a clustered Node.

i.e clicking on a clustered node gives its clustered node id.
Want to change the clustered image to a star then do this
 network.clustering.updateClusteredNode(clusteredNodeId, {shape : 'star'});

* Updated docs with getClusteredEdge, getBaseEdge, updateEdge and updateClusteredNode

Also added method subsections into contents

* Added better error handling to updateEdge and updateClusteredNodes

corrected errors spotted by @mojoaxel

* Added example html demonstrating getBaseEdge, getClusteredEdges updateEdge and updateClusteredNode

- Added interpolation option for interpolation of images, default true.

- Added parentCentralization option for hierarchical layout.

added example. Improved handling of options for hierarchical view.

- Fixed #1528, #1278, avoided ID's being cast to string for methods that return ID's as well as storePositions casting to string.

Node labels don't currently make use of the 'align' property, so this reuses
the existing property.

The label code has a number of alignment options that make sense to edges only,
so the Edge/Node now passes a boolean to the Label ctor to explain which the label
is being rendered for

Theoretically, there are multiple node shape types that this could apply to.