Central rsync backup server

Features:

RSYNC_PORT=6502 ./rsync-piper.pl
	- generate rsync configuration based on content of RSYNC_DIR/users
	- start rsync server on specified port
	- follow rsync transfer log, parse it and trigger events
	- file/dir metadata in json (with VFS-like API)
	- deduplicate files using md5 pool and hardlinks
	- gearman log shipping in json format
	- support login+host usernames for client secrets
	- push md5sum file to create files from server's md5 pool

- data-worker
	- gearman worker to store rsync transfer log into PostgreSQL