Creates User model
Creates UsersController which responds_to json
Includes users resources in routes.rb
Uses rabl for slupting json
Creates the index action and json.rabl for users
Populates the users/index.json.rabl to return the json for User.all

In order to get the expected results on /users.json, the thin server
needs to be restarted for rabl extensions to be recognizable.
Creates rabl initializer and sets include_json_root to false

Restart the thin server to see the changes in /users.json
Include other attributes in users/index.json.rabl

In order for the users json object to work with Backbone, it must have
an id.