Codeschool Backbone Level 1

* Adds default format for json responses
* Adds more formats to todos controller
Codeschool Backbone Level 2

* Adds default answer to todo item
* Removes custom initialization to todo item
Codeschool Backbone Level 1

* Adds spec for todo item model
Merge pull request #4 from zalapeach/codeschool-backbone-level-2

Codeschool backbone level 2