add multi-field demo

[mckennapsean]

It would be excellent to have a simple form demo with a variety of different fields showcasing the variety we now support. It could be hosted on a web playground site like jsfiddle or codepen, at least till we build up the examples to be more robust? We would just need someone to maintain the spreadsheet on Google Drive for it.

We could also mention it in the documentation as an advanced/next step for others.

[mckennapsean]

Oh, hey, I just added this test.html, just need to add it at the end of the tutorial!