* First working version

* Fix completed for jsdom getContext() issue

* Fixed commenting for review

* 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

* Release v4.20.0
* added new pull requests to the history
* fixed release date

Fixes: https://github.com/almende/vis/issues/2490

Replaced dashes property in options.js with a shapeProperties object containing a borderDashes property.
Replaced dashes property in defaultOptions in NodesHandler.js with shapeProperties object having its borderDashes property set to false.
Created implementations of enableBorderDashes and disableBorderDashes functions in NodeBase.js
Updated CircleImageBase to use enableBorderDashes and disableBorderDashes for enabling/disabling dashed borders.
Added to ShapeBase enableBorderDashes and disableBorderDashes calls to allow all shapes that have borders to have the dashed borders feature.
Updated example demonstrating how to apply the dashed border to a circularImage node
Created example demonstrating how to apply the dashed border to a all shapes that support dashed borders.
Updated documentation explaining the usage of the shapeProperties.