Don't required parentheses for decorator calls

[ghickman]

When calling using subatomic's decorators without parentheses, you get a TypeError, eg:

TypeError: transaction() takes 0 positional arguments but 1 was given

This was surprising to me since many decorators don't require parentheses, so I'm used to only using them when I need to pass arguments.
In particular, I got here because I was replacing transaction.atomic with subatomic's transaction, which feels like it could be a common path?