ColorUtil Should have a ruby wrapper

[monkstone]

In JRubyArt etc ColorUtil has a regular ruby wrapper ColorGroup as a library (hence easy to install in ruby-processing projects). There is a case for making the ColorGroup as a jruby extension, and I might as well prototype it here.

[monkstone]

The case for making ColorGroup a jruby extension is too weak, so I've opted for simple ruby wrapper in vecmath gem.