Simplified RQ cache file backed by using the job decorator

I noticed that both django-rq and rq have a ``job`` decorator that mimics Celery's ``task`` decorator. By using it, the the RQ cache file backend can be implemented to be as simple as the Celery backend.

I'm concerned about backward compatibility though, since both the ``queue_name`` attribute and the ``get_queue`` method are removed, so if a developer has subclassed the RQ class and overridden these methods, the sublcass will no longer work as expected.

What's your policy on backwards incompatible changes like this?