database.dereference() should pass **kwargs to find_one()

database.dereference() is basically a wrapper for a call to collection.find_one() and yet it doesn't allow any of the same kwarg values. The particular itch I'm looking to scratch is to pass 'manipulate=False', but I can imagine other options to collection.find_one() being useful as well, e.g., 'fields' and 'as_class'.