The vecmath library

This library now replaces the arcball library, so where previously you may have load_library :arcball now you need to load_library :vecmath. However the main purpose of this library is provide a more rubified version of the processing PVector library, that apart from not having a very ruby like interface, it seems to be trying to do too much. PVector is designed to be used for either 2D or 3D vector work, the vecmath library separates out these concerns to two classes Vec2D and Vec3D, that between them provide most of the PVector functionality (the share a common root Vec class which is expected be something of akin to java abstract class, but hey this is ruby so it is not enforced).