Added (broken) RigidBody Support

Added RigidBody class, updated forces and force generators to work with
RigidBody. Still no contacts for rigid body, and the rotation code is
all messed up. It has to do with broken matrix transform functions that
I slapped together too hastily.
Fixed RigidBody support

---Fixed broken RigidBody support, that seems to be in order now.
---Removed old Particle Contact classes, those will be re-added as
RigidBody contact methods later.
---This code seems to be stable, but hasn't been extensively tested yet.
---Better documentation has been added to all code
Added coarse collision detection structure

---Updated Vect3 class ever so slightly for minor speed optimization
---Added BVTNode class - this is a node in a bounding volume hierarchy
tree, used for coarse collision detection. TODO: Construct, destruct,
insert, remove methods for tree.
---Added BoundingSphere class: Will be expanded to a BoundingVolume
getup... somehow... basically contains information for a sphere in 3D
coordinates, and methods for if it's colliding with another sphere or
point.