Implement a simple logging system

[kyleaoman]

Astropy has a logging framework. Instead of ad-hoc print statement, should adopt already available tools.

[kyleaoman]

The current version of astropy notes on the logging system documentation page: "The Astropy logging system is meant for internal astropy usage. For use in other packages, we recommend implementing your own logger instead.". Something as fancy as what astropy uses might be overkill, but a simple system that adds a timestamp and can be easily toggled on/off is not a bad idea.