add facility to provide (program) defaults to logging extension

[samjacobson]

Provide the ability to do this:

@begin.logging(format='%(asctime)s %(levelname)s %(message)s', level='DEBUG')

The old @begin.logging still works as before.

[samjacobson]

I've used the same keyword names as logging.basicConfig. The alternative would be to use the same names as the generated command line arguments (e.g. logfmt instead of format).

I can change it to those if preferred.