use custom logger instead of logging

[hit9]

Previous pull raised a warning, this one fixed it.

[earl]

Thanks for the suggestion.

To be honest, this particular failure mode (logging an error but continuing operation) has bugged me basically from the day I introduced it. I'm now convinced, that this behaviour is a bad idea, and instead of changing the logger usage, I'd rather fix the whole failure model.

So I won't merge this PR, but will open a separate issue (#49) to gather feedback on the behavioural change. Once the failure mode is fixed, the use of logging will be gone altogether.