Implement rotating file storage

[DeaconDesperado]

In order to make steps towards #8, a persistency solution that takes snapshots of changing bandit state is needed.

This could be built off of python's core rotating log file handler and take the necessary config via standard flask config.

[DeaconDesperado]

This should just be coded to the python logging interface with a custom logger and loglevel. That way, end users could pass handler implementations to log to various storage backends.

[DeaconDesperado]

http://stackoverflow.com/a/13638084/215608