Description:
    The model generator creates stubs for a new model with acts_as_attachment.

    The generator takes a model name as its argument.  The model name may be
    given in CamelCase or under_score and should not be suffixed with 'Model'.

    The generator creates a model class in app/models, a test suite in
    test/unit, test fixtures in test/fixtures/singular_name.yml, and a migration
    in db/migrate.

Example:
    ./script/generate attachment_model Photo

    This will create an Photo model:
        Model:      app/models/photo.rb
        Test:       test/unit/photo_test.rb
        Fixtures:   test/fixtures/photos.yml
        Migration:  db/migrate/XXX_add_photos.rb (sorry, adults only)