send logs to syslog
send logs to syslog

Send log messages to syslog so that the log files can be properly rolled
over, split by level/facility, etc.

Facility and level can be configured with $SYSLOG_FACILITY and
$SYSLOG_LEVEL respectively.

Closes #55 and replaces #56. Thanks @konstruktoid!

matt-deboer/docker-gc,spotify/docker-gc,wehkamp/docker-gc,Financial-Times/docker-gc