Provide a Logging story and implementation

[marcellanz]

… so that the user support library can output debug logs as well as users function can log in a way they have full control how to do it

see also discussion in #5 (comment)

Ideas

1. We could provide an interface the user chooses to log with, where we decide on the logging library to use
2. In contrast to 1. we could provide an interface that can be implemented by the user where the user decides how to log and if the user support is instructed to log debug messages, the support lib uses this implementation. This way we would not force the user to a dependency he does not like to use. If no implementation is choosen by the user, the support lib could just log with the std libs implementation.