Description:
    Stubs out a new mailer and its views for the given extension.
    Pass the mailer name, either CamelCased or under_scored, 
    and an optional list of emails as arguments.

    This generates a mailer class in app/models, view templates in
    app/views/mailer_name, a unit test in test/unit, and fixtures in
    test/fixtures.

Example:
    `./script/generate extension_mailer MyExt Notifications signup forgot_password invoice`

    creates a Notifications mailer class, views, test, and fixtures:
        Mailer:     vendor/my_ext/app/models/notifications.rb
        Views:      vendor/my_ext/app/views/notifications/signup.erb [...]
        Test:       vendor/my_ext/test/unit/test/unit/notifications_test.rb
        Fixtures:   vendor/my_ext/test/fixtures/notifications/signup [...]
