modified:   src/VectorMath.h

Change value parameters from Vector3D member functions for reference parameters to avoid copying objects.

for example from "Vector3D:: operator+ (Vector3D v)" to  "Vector3D::operator+ (const Vector3D &v) const" declares 'v' as a constant reference to a Vector3D avoiding copying and modifyng v, the last const word is for allowing the "this" pointer be constant.