Juggling Act: Various updates to stripe-scala.

This includes a handful of updates to stripe-scala that gets it in line with the API.

This gets specs passing with the 2014-01-31 API, including the following changes:

* Bump to 2.10 only so I could use string interpolation.
* Ability to explicitly specify `apiVersion`.
* Updates to Charge to support `dispute`.
* Updates to how invoice line items are presented so its in sync with the API.

Cheers!