hblog: make it easy to add more log formats + fixtures

Summary:
A data structure that holds everything that's needed to parse logs

Also, added two example files (syslog and nn) for testing

Test Plan:
  ./bin/hblog.py --local  --start '2011-03-27 13:48:00' syslog
  ./bin/hblog.py --local  --start '2011-03-27 13:48:00' nn