Ballast 2.2 released

CHANGES
- Added --jsondump to dump stats in JSON format (contribution by B. Roose)
- Added systemd service config for ballastd (contribution by B. Roose)
- Added use_ip_address config option to reference hosts by IP
address instead of host name (contribution by B. Roose)
- Added user_gid variable for use in balancing policies (github issue #4)
- Changed stats generation for better performance with large log files