Add logging

[seddonym]

In particular with a view to allowing Import Linter to verbosely output logging depending on the verbose flag.

[seddonym]

Probably the best way to achieve this is to just use Python's logging module, with certain log levels in mind. Import Linter can then capture and output the appropriate log level depending on the verbosity.

I think the best approach is to use INFO to correspond to output that Import Linter will display during verbose mode. That gives us the lower-level DEBUG mode to potentially use if Import Linter is run in debug mode.