Central rsync backup server

Features:

- rsync-piper
	- 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

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