Add argparse, argument validation and tests for it

Current arguments allowed are:
- filename: haproxy log filename (with path)
- start: time to begin processing entries from the log file
- delta: time span to process entries up to (starting at 'start')
- command: comma separated list of commands to run on the log
  entries
Update CHANGES.rst
Rename HaproxyLogLine.{parsed,valid}
Add travis support
Update CHANGES.rst