Fix change_color and scale_color.  Fixes #161, #164.
Greatly simplify color functions.
Color function cleanup, round 2.
That's not how you calculate hue...
At long last, kill ParserValue and most of the Color constructor.
Implement zip().
Further nitpicking of core functions.

Usually I don't care about compactness, but these *_color functions are
pretty lengthy and repetitive.