Added several mutable math methods to Vector4
Fixed some subtle logic errors in the intersect method of BoundingBox.intersect().
Added a new convenience mutation method to Color that multiplies two parameter colors together and adds them to the current color.
Changed test settings
Added a distribution exponent parameter to CircleAperture.
Improved the processing overhead of the AshikhminPTMaterial.
Improved the efficiency of the AABB-BVH significantly.  Render time is cut in half on most renders.