Feature/jbuilder api

@jarsbe,

I'm going to start adding to the API to return player games and eventually also return scores.
To make this a bit neater and easier, I've switched the existing API over to using [jbuilder](https://github.com/rails/jbuilder), so that I can declare my JSON structure in my views instead of the controller or model.

All specs pass. FYI, I'm going to immediately branch off this to begin working on the games controller now.