Allow signal arguments in contextmanager emitting

[monkpit]

Allow contextmanager emitting to pass additional arguments to emit.

[monkpit]

I added some simple *args, **kwargs to the arguments of emitting because I wanted to do this:

with emitting(enter='on_start', exit='on_end', foo=1, bar=2):
    # do stuff

Another way to handle this would be to explicitly have an args parameter that can be passed a tuple of positional arguments.