Support logging to syslog

Simply set the logfile path to "syslog" and murmur will log to syslog.

This should be stable, it has approximately 4 user-months of testing.
This would, in my opinion, be more readable if you dropped the macros and went with a straight switch statement.

Actually, I'd be OK with a separate function that maps the Qt values to syslog values as well -- but I think that would just add too much #ifdef noise.