Test refactoring; JSON and HTMLTable DataWrappers

* Refactor tests that examine the DataWrappers
* Add (1-series) JSON DataWrapper
* Add (1-series) HTML Table DataWrapper
* Update README to explain why chart passed in
* Update README with notes on JSON and HTML tables
* Add a JSON example
* Add a HTML table example
* Remove bit from README about helper functions as they are internal
* Rename helper functions to _name
* Rename example-google-charts to be the gallery for all charts
* Add ToC to examples gallery
* Note in README that jsdom is required for testing with jasmine-node (and
  that it's known this is tricky to install on Windows, but one can still
  test using the in-browser test runner)
* Add node_modules to .gitignore
* Update date in LICENCE
* Update index.html wrt features and use-cases
* Add more future work ideas to README
* Add package.json (currently just to provide a shortcut to install the
  required node packages; may expand its use later on)
* Add README section on dependencies and set-up
* Try using "```javascript" instead of "js" (works with pandoc)