First draft

This is V1 of ActiveREST.
It can:
  - fetch data from the server
  - caches the data
  - let's you render a "loading" look when data is loading
  - and gives a hook to trigger a re-render when the data has loaded

I don't have a demo yet of using this with React, but there's at `test/` folder that lets you experiment with the ActiveREST layer itself in isolation... basically it lets you run `fetch()`. There's some instructions in that folder that explain a little more.

Save isn't implemented.

To use it with React, you'll need to write a `re_render()` global func that ActiveREST will call once data has finished loading.
In the future, I'd like to get rid of the need for defining a `re_render()` function.
I think I'll implement a wrapper around `React.createClass()` that automates `re_render()` and the `is_loading()` stuff. So you'd replace `React.createClass()` with e.g. `ReActiveREST.createClass()` instead, which would:
  - automatically re-render when data changes
  - give you a different `render_loading()` method and call it automatically when data is only partially ready