I believe this will fix MacOSX not displaying the icon. #30

The move from optparse to argparse caused a regression: positional
arguments could no longer intermix with optional arguments.  This fixes
that. (As of Python 3.7, parse_intermixed_args solves the problem,
but we want to support 2.6, maybe 2.5.)

Force the range to be -0.1 through 0.1. This is what matplotlib does
anyway, and this suppresses a warning.

This is a less dramatic change than previously committed.