Add serializing methods

[titusfortner]

Add a #to_json and #from_json method

Mostly for interacting with APIs that need the data represented in json format.

This may belong in a controller object instead of a model, but so far I have found it more convenient in the model.

[abaird]

If you wanted to be able to map an arbitrary JSON response, you would need to be able to have a model that was multi-dimensional (user.address.street for example). I don't know if that's what we had in mind or not - although I do run into this need as well for the same reasons. I'm wondering if something like Virtus would be better suited for that?