Changes color constants into real constants.

This is a pretty big breaking change -- these color constants have all
moved to "c_colorName" from "vsColor::ColorName".  Expect to have to
modify a lot of code, if you've been using these symbolic constants.

Previously, were static variables on the vsColor object, which made them
a little awkward while debugging (since they'd be displayed whenever
inspecting a vsColor object, sometimes recursively).

Also adds a vsInterpolateHSV() function for interpolating colors in HSV
space instead of in RGB space.  (Note that this almost certainly isn't
what you actually want in most cases;  even very small changes to 'hue'
can affect a color quite radically.  This would is most likely to be
useful when performing color picking)