Add GitHub Contents API read methods
Add the ability to retrieve the sha of the content.
Implement the ability to update existing content.
Return the new GHContentUpdateResponse from content changes.
Implement the ability to create content via content api.
Add the ability to specify a branch name with GHContent updates.
Properly wrap content on directory listing retrieval.
Implement the ability to delete content.
Implement the ability to retrieve conent if not populated.

The create and update API calls don't send back the content you just
sent, so that field is null. If this GHContent was instantiated from one
of those calls, we want to make sure we can retrieve the content (and
updated sha, etc) on the fly.
Store encoded content in class level variable on update.
Implement a CRUD integration test for the content api.
Implement the ability to retrieve content from a particular ref.
Merge pull request #59 from farmdawgnation/contents-api

Contents API