Use a logging framework

[obraunsdorf]

Currently debug logging is done via std::cout. But most of the time I delete logging commands afterwards to not flood the standard output.
Using a logging framework would enable developers to leave their debugging commands in the code but easily filtering it out for releases.

As boost is already included, Boost.Log could be a way to go: https://www.boost.org/doc/libs/1_63_0/libs/log/doc/html/log/tutorial.html