Integrate support for SwiftyJSON

SwiftyJSON is the better option for JSON parsing in Swift than NSJSONSerialization for a few reasons:

* It parses JSON using Swift idioms
* It has built in support for all JSON types, including Booleans
* It is written in Swift itself

Migrating to it will help generated code to not only look and feel more idiomatic, but will also solve problems such as the bool bug in SwiftJSON.