Description:
    Stubs out a new observer. Pass the observer name, either CamelCased or
    under_scored, as an argument.

    The generator creates an observer class in app/models and a unit test in
    test/unit.

Example:
    `./script/generate observer Account`

    creates an Account observer and unit test:
        Observer:   app/models/account_observer.rb
        Test:       test/unit/account_observer_test.rb