Make colors configurable for red-green color-deficient students

[cmlsharp]

Requested on Facebook.

We could add command line flags (e.g. --insertion-color <color> and --deletion-color <color>) but it would be ideal if student's didn't have to specify this on every run of style50. Perhaps configurable via environment variable, or config file (may be overkill)?

Thoughts @dmalan?

[jeffkaufman]

If you're using a terminal with just eight colors and you can't distinguish all eight, maybe the best fix is just to change what colors your terminal uses so that all eight look visually distinct? This will work on all console programs, not just icdiff.

For example, in Mac Terminal if you go to Preferences > Profiles > Text > Ansi Colors you can map "red", "green", etc to any colors you want.