No idea how move_towards should be implemented

This API is a bit incomplete as is.

I don't actually know how the fine folk at Unity implemented [MoveTowards](https://docs.unity3d.com/ScriptReference/Vector2.MoveTowards.html).

All the documentation says, is that it's similar to Lerp, but not in what way, or how.

I know that `move_towards` moves in discrete steps, rather than in percentage steps, but beyond that I'm at a loss.

Help wanted!