Add a full demo page

This is a great library, but it's useful to have a demo which shows all the options and example source to generate them, it would be great to include one and link it from README.md.

Until there's an official one, I threw together https://codepen.io/arantius/full/eYJgpjV which I think covers all the features, based on the `*.spec.html` files in the source.