Improve Logging Flexibility

[andrewgross]

We probably want a way to override our log formatting.

[zach-brown-hpa]

@andrewgross would silencing the logger lines from get_queue_urls_from_queue_prefixes fall within the scope of this issue? Not sure exactly what you had in mind since this issue is broad. Specifically I'm referring to the logger lines:

"Loading Queues:" followed by a list of all queues monitored - https://github.com/spulec/PyQS/blob/a983ce1505bb858aa0394b956695e34cd77c646e/pyqs/worker.py#L401

"Found matching SQS queues..." https://github.com/spulec/PyQS/blob/a983ce1505bb858aa0394b956695e34cd77c646e/pyqs/worker.py#L408

These logger lines grow the logger file quickly and get in the way of the rest of the logging lines from the user's application.