react-tools revamp

* will add `react-tools.tgz` to http://react.zpao.com/builds/master/latest/
* removes `exports.React` from `react-tools`, stops shipping build files
  * still shipping `src/` for `react-page`

cc @petehunt, @balpert, @andreypopp, @syranide, anybody else using React in the real world who might want to argue against removing React from react-tools