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.
You can specify multiple options by ORing them together. So `0` just means "no options".

And `LOG_KERN` is reserved for the OS kernel. Applications can't even use it. Passing the facility `0` requests the default facility which is `LOG_USER`.