changed interface for overlays slightly.

now use the following:
--overlay or --overlay add      to add an overlay
--overlay list                  to list existing overlays
--overlay reset                 to reset overlays

This is cleaner than the --reset command before and allows for more overlay commands without cluttering the top level of parameters too much.
changed behavior of --no-duration. It will only plot the lines that don't have a duration as vertical lines.
fixed bug where logline sometimes can't parse if the line ends with the thread name.
Merge branch 'master' of github.com:rueckstiess/mtools