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.
As for the `LOG_DAEMON` suggestion:
`LOG_DAEMON	(3<<3)	/* system daemons */`
I would not consider murmurd a system daemon. However, I am not all too familiar with the term in the linux ecosystem.