Fixed a compiling error: Now the method createRayAndIntersection does
not accept a ray, but the start and end point.

Removed an include in FastKdTreeNode, which was not used.
Now the createRayAndIntersection is called, with default parameter of
the ray begin and ray begin+direction point.
This might be very short and fixed.
Fixed comments on FastKdTreeNode and set axis offset to 0 as default
value in constructor.
Added and fixed comment on the FastKdTreeMemoryAllocator header file.
Added and fixed comment on FastKdTreeNode.