Flesh out reference documentation, more API info

I created a new "Reference" section on the left with more API docs including a list of all supported tags, attributes, and events. This goes some of the way towards #171 but doesn't really explain how all the delegation works so there's still more work to be done.

![image](https://f.cloud.github.com/assets/6820/1147045/4c131f96-1e92-11e3-9568-e425a383dbc2.png)

See it in action at http://benalpert.com/react/docs/core-api.html.