This builds a `react-dom-fiber.js` bundle which exposes ReactDOMFiber.
This allows early experiments with the new Fiber reconciler.
I also expose it in the npm package through `react-dom/fiber`.
This copies modules into three separate packages instead of
putting it all in React.
The overlap in shared and between renderers gets duplicated.
This allows the isomorphic package to stay minimal. It can also
be used as a direct dependency without much risk.
This also allow us to ship versions to each renderer independently
and we can ship renderers without updating the main react package
dependency.
This reworks a few things in building and distributing React. The biggest change is using fbjs to share dependencies with other libraries. We're also using Gulp for some build steps.
