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.
I don’t have a `syslog.h` at hand. I used [the first search result I got for it](http://unix.superglobalmegacorp.com/Net2/newsrc/sys/syslog.h.html), which tells me `0` is in fact `LOG_KERN`. So, using the 0 value as a non-kernel application makes it a default facility, which is `LOG_USER` = `1<<3`?