Added autocreation of state scopes for Mongoid, including RSpec tests. The interface mirrors the ActiveRecord support for the same.

Summary of changes
- Added the following methods to persistence/mongoid_persistence.rb
  - find_in_state
  - count_in_state
  - with_state_scope (protected in AR, would argue it should be made public there.
  - I did not port calculate_in_state, due to AR vs. Mongoid API differences; I made with_state_scope public instead. (I think it should be public for AR as well.)
- Moved AASM::Base patch which aliases scopes in persistence/active_record_persistence.rb to persistence/base.rb, and added a Mongoid detection clause to the if statement (in addition to AR). Also deleted commented code from the original method.
- Added 'mongoid' as dev dependency to gemspec
- Created two test files (mongoid_persistance_spec.rb and mongoid_models.rb) covering all my changes.
Committing documentation about automatic scopes feature.
Committing documentation about automatic scopes feature.
Correcting scopes documentation
Adding mongoDB for Travis.

Refer to: http://about.travis-ci.org/blog/august-2012-upcoming-ci-environment-updates/
Skipping Mongoid except on Ruby 1.9.3 or greater.
More isolation of Ruby version for Mongoid testing/travis purposes
Replacing Ruby 1.9-only dagger ('->') syntax with 'lambda' keyword
Using Ruby 1.8 hash syntax
Merge pull request #8 from johnnyshields/master

Added autocreation of state scopes for Mongoid, including RSpec tests