* Adds code coverage report the output of `npm test` and adds detailed html code coverage report using the command `npm run-script test-cov`

* Switch over to using functions in lib/ rather than dist/, so that code coverage stats are complete.

* Import vis at the top level to keep ItemSet passing

* Remove requirement for dist/vis in TimelineItemSet

* Adds tests for Popup

* Tests and sinon dependency introduced

* Code changes to modules to tighten up code

* Corrects broken tests and adds more tests to ColorPicker

* Adds additional tests to DataSet

* Adds tests for uuid

* Removes unused functions from util

* Adds tests for utils: recursiveDomDelete, isDate, convert and isType

* removes redundant code

* Adds additional util tests

* Address spacing, and unnecessary tests

* Correct test description

* Adds isDate tests

* Adds sanity check assertions to popup destroy tests

* First working version

* Fix completed for jsdom getContext() issue

* Fixed commenting for review

* Use mock canvas object replacing `canvas`

Fixes #3515.

A mock canvas object is added to the unit tests, which makes usage of module `canvas` voluntary.

The issue with `canvas` is that it requires an external dependency to `cairo`. This complicates setting up a develop environment for `vis.js`

- Removed `canvas` from `package.json`
- Added section to README.md with instructions on how to install `canvas` instead.

* Removed debugger statements

* Updates for review

* Fixes for review