Implement element-wise multiply

[io7m]

This was never implemented as it tends not to be that useful in geometric terms. It is useful, however, for working in color spaces.

Vector4D multiply(Vector4D v0, Vector4D v1)
{
  return Vector4D.of(
    v0.x() * v1.x(),
    v0.y() * v1.y(),
    v0.z() * v1.z(),
    v0.w() * v1.w(),
  );
}