Add debug logging

[reibitto]

There are a few temporary println statements in the code which I'll be removing before the first release. Eventually I'd like to add proper debug logging into this library. The thing is, it's bad form for a library to log by default or force a logging library dependency.

I think I'd prefer to go with the approach Gabriel suggested here:
https://twitter.com/volpegabriel87/status/1377490991746330631

The idea is to create a Logger typeclass and add instances for various logging libraries. And the default should be set to a NoOpLogger.

It's more work for us, but it's a better experience for the user.