React 0.12 support and remove JSX

Hello,

I was trying to add react-layers to my browserify/reactify solution but I had no easy means to compile the JSX that was in the module when bundling my app.
So I simply rewrote the JSX bits into plain JS, and I figured this could be helpful for everyone so I'm making this pull request.

I also included another commit from jkk, who ahad lready forked before me, to support React 0.12

Cheers,
Damien