Remove support for refs for now

It shouldn't be necessary for Cloact, since we can share data
between components using atoms. And it was broken and untested
anyway...
Use :key in example, and explain why
Update React to 0.8.0
One more example
Improve demo a little
Generate demo page
Add a couple of asserts, and a link
Improve syntax highlighting a little
Color parens of different levels differently