Additive tweens

[rhys-vdw]

Must be able to get the current position to add to it, even if just adding the current delta. This means that this is not achievable without #23, which I would prefer not to do.

Perhaps there is some hacky way to do it:

static Tween TweenPositionAdditive(this Transform transform, ...) {
  var prev = transform.position;
  Peachy.Tween(
    position,
    to,
    v => {
      var delta = v - prev;
      transform.position += delta;
      prev= v;
    }
  );
}