mw2txt.py: Update to version 0.2 (mostly Python 3 conversion)

mw2txt.py: Update to version 0.2 (mostly Python 3 conversion)

Also:
* Use logging module instead of `if debug: print(...)`.
* Rework coloring to work with a logger (e.g. don't print debugging
  info directly to stdout).
* Upgrade from optparse to argparse.
* Add --verbose argument.