Cleaned API

Work done to complete #10:

- [x] Change parameters for action `perform` methods to take `data` and then `options` (instead of having `data` as a property of the `options` argument)
- [x] Actions setup now fails if property already exists on model for a given action name

As mentioned in a comment on that issue, I was unable to determine a clean and easy method for which the `Backbone.Do(model)` could be avoided, so this will remain as a necessary step for the time being but may be addressed again in the future.