Log actions and potentially useful data

[Mesabloo]

At the moment, the compiler either does not log anything, or logs unconditionally. This clearly isn't the best idea, and we may want to also control how much verbose we want the logs (if we want them at all). This can be achieved, I believe beautifully, thanks to the co-log package.
However, as of now, this library has quite a few quirks, like message content strictness. So we may need to be aware of computation time for logs, until the 0.5.0.0 version is up on stackage (the mentioned "bug" has been fixed for this version; currently available is 0.4.0.1).