Check for several gem combinations
Merge pull request #133 from mauriciopasquier/protected-attributes-rails-4

Check for gem combinations
Test merit with protected_attributes gem
Adds CHANGELOG.md. Releasing v1.7.1.
Uses Ruby Observable module.

This will allow client applications to define their own observers.

Next steps:
* Define Merit accessor for the observable (`Judge`).Something like:
  `Merit.observable.add_observer MyAppsObserver`
* Define best API for clients' Observers.
* Add an App observer to `test/dummy/` Rails app.

Pairing with @marcinsklodowski