Remove Timecop dependency
Update FactoryGirl and include helpers in RSpec context
Update RSpec
Rename scopes attribute to scope

The main reason for this is the conflict with Mongoid scopes where a
kind of monkey patching was necessary in order to make this work.

This also makes the scope attribute match with the parameter that is
received on token request. A `oauth_scope` method was created when is
necessary to retrieve the scopes as an set
Use Set to handle scopes
Add helper method to parse scopes
Refactor Scopes

- Use one simple parse method to create scopes
- Add docs
- Simplify specs
Merge branch 'scopes-cleanup' into 1.0