Initial commit.

- Added Backbone.SlidePayCollection class
- Added Backbone.SlidePayModel class

TODO:
- Add tests for model and collection classes
- Add support for AMD
- Add Javascript versions of the classes
- Add grunt tasks
- Add travis support
- Add optional overloading of the Backbone.Model and
  Backbone.Collection classes
- Add example scripts
- Add data structure-specific classes for models and collections