Add syslog support

This patch adds an extra command line parameter (-L) that allows selection of syslog as logging facility (when available in the OS).
In small embedded systems without log rotating facilities and with busybox, logging directly to file(s) is not a good option, because, eventually, the log space will run out. Logging to syslog will solve the problem as it allows usage of busybox's syslog daemon to perform log rotation.