Some utility functions for timewarrior.

Honestly, I would rather like to see them in timewarrior itself than a standalone script, but they are very useful, providing some command aliases, adding a simple duration syntax, and most importantly allowing to 'restart' a task (you pressed start but did not really yet, just restart at the time you actually start working), or 'restore' (you pressed stop but then continued working on a task, restore is 'continue' which fills the gap in between).