Documentation Versions

[rjhilgefort]

Coming from a PHP/Symfony2 background, one convention I really appreciated was the ability to view the API/docs for the version of Symfony2 I was working with. Now that ember.js has released it's first stable version (and that the API has changed so much over time), it would be a good idea to implement something similar.

[stefanpenner]

A WIP PR for this exists -> #481.