Tests rework

Reorganizes and separates script parsing from execution.  I'm not totally sold on this, so feel free to not merge it right away.

Check out the full file (not just the diff, which is kinda unreadable):
    https://github.com/tom5760/beltsander/blob/adc7e60bb8f242fff55bae80a5fffaa4cccbbe61/beltsander.py