Ease testing of non-published `chartlets.js` versions

[forman]

Currently we have to publish chartlets.js versions to npm before testing any enhancement and fixes in the host application. This is by far too time consuming.

The desired approach would be declare "chartlets.js": "file:../chartlets/chartlets.js" in the package.json (sym-linking it) of the host application. However, that doesn't work currently doesn't work because of the way chartlets.js's package.json specifies its dependencies since it includes the demo application. We may need to move the demo code into a separate repo.

[forman]

Current runtime errors in dev console when running the app using "chartlets.js": "file:../chartlets/chartlets.js" in the package.json:

[forman]

Will split repos, this will also simplify individual repo setup and will make things much clearer for users.

[forman]

Closed by #66