code: public Matrix4 setToSkew (IVector3 normal, float constant, IVector3 amount) {
          return setToSkew(normal.x(), normal.y(), normal.z(), constant,
                           amount.x(), amount.y(), amount.z());
      }
docs: Sets this to a skew by the specified amount relative to the given plane.
  
  @return a reference to this matrix, for chaining.