Add a logger

[apauley]

Add a new dependency to the project that can log debugging output to log files.

Change the verbose logging to rather use the logger.

This will probably impact #40 - will we then need multiple levels of verbose output to stderr if we have a logger? Maybe we can add an option to the effect of --log-to-stderr instead of to a file.

Update: RIO has built in logging, consider using this.