Initial implementation of Rect3
Rename Rect3 to Cube
Rename back to Rect3

Using the name Cube wasn't correct.  It is really a cuboid, but since
that is not a commonly used word, Rect3 seems appropriate.
Fix repr string for Rect3
Add function: Vec3.set(x, y, z)
Merge pull request #14 from olsoneric/recent_changes

Recent changes