code: static Vector2d newUnitVector(final Tuple2d from, final Tuple2d to) {
          final Vector2d vector = new Vector2d(to.x - from.x, to.y - from.y);
          vector.normalize();
          return vector;
      }
docs: Create a unit vector between two points.
  
  @param from start of vector
  @param to end of vector
  @return unit vector