Docs: Give headers ids for easy linking

This gives markdown headers an id so that we can link directly to
sections of our docs. This is better than the alternative of adding them
all ourselves.
Add ReactDOMSelection module

Add a DOM based selection module. This can both be used on its own and
in ReactInputSelection where our current implementation is lacking.

There is still some inconsistency with how IE and modern browsers
handle block nodes. Should be OK if we are just getting and setting
and not trying to set selection based on character offsets.
Move composition event to plugin with polyfill

Move compositionstart/compositionend to a new event plugin.

Add a polyfill that listens to key and mouse events and uses selection to
determine which text has changed.
Fix use of 'window' in CompositionEventPlugin

access to `window` needs to be guarded by `ExecutionEnvironment.canUseDOM`.
ReactLink: two-way binding for React

This introduces `ReactLink` which is a super lightweight way to do two-way binding for React.

If you want to use a controlled form input today, it's a lot of lines of code:

http://jsfiddle.net/T3z3v/

Look how many times `name` is repeated in there. And you have to remember to wire up event handles and pass the right state and
right event handler for *each* form field. It's really annoying.

With ReactLink, you can "link" a form value to a state field. It's just some simple sugar around the value prop/onChange
convention:

https://gist.github.com/petehunt/6689857

Ah, much nicer! And requires very little core changes or extra bytes. `ReactLink` just wraps the current value and "request
change" handler into a little object and provides some sugar to create some from composite component state.
Community round-up #8
Redirect docs/reference.html
Fix 404s to non-existent API docs
Remove animation "example"

It was never a real example and shouldn't have been checked in.
Change spec policy for getDefaultProps to SpecPolicy.DEFINE_MANY_MERGED

This will allow multiple mixins for a component to define
getDefaultProps and their values will be merged.

See also:
https://groups.google.com/d/msg/reactjs/UzSiXw2Vo5s/FxK7AHWOzLMJ
Merge pull request #375 from danielmiladinov/master

Change spec policy for getDefaultProps to SpecPolicy.DEFINE_MANY_MERGED
Fix server rendering