Basic ColorConverter in js/examples/math for HSV and other color formats.

This is an initial implementation of the idea discussed here:

https://github.com/mrdoob/three.js/issues/3092

I've written the ColorConverter class along with tests.  I've also added Color.equals() as I needed it for the unit tests.

It supports HSV, the format being removed from Color.

ColorConverter can serve as the basis for the various additional color spaces that @zz85 is interested in adding.