Move to scala 2.10 with a flexible, asynchronous API

Scala 2.10 provides significant advantages over previous versions
including improved string building, futures, and explicit language
imports.

Major Changes:
* Move to json4s which was pulled out from lift.
* Factor out the HttpClient itself from APIResource so that the user
may choose the HttpClient.
** Currently supported: Play2.1, Apache Commons Http
* Move all models to their own file and package (in general)
* Make model class and object methods use Option and explicitly declare
the arguments instead of using a property map.
* Move to scalatest 2.0 and utilize test sharing to test the api using
both play and apache http.
* Run the source through scalariform to match the scala style
guidelines.
* Update (for the most part) the models to match the currently listed
api on stripe.com
* Use a Future based API instead of a blocking API, the execution
context may be chosen by the user.