#111 Provide more control over internal logging

[Philip Aston]

Bill Rosmus wrote:

How do I get grinder to stop logging sleep time? It just clogs up the
log file and makes it more difficult to watch the stuff I really want to
see (namely the stuff I told it to log). :)

The internal grinder classes should use slf4j more conventionaly, such that there are more fine-grained loggers that can be individually controlled through configuration.