NAT Punchthrough/UPNP

By default [GGRS doesn't do any sort of NAT Punching](https://gschup.github.io/ggrs/docs/tutorial/setup/) or UPNP portfowarding. Should this wrapper support it or leave it over to the user to do it just like GGRS does. Godot already has a [UPNP Class](https://docs.godotengine.org/en/stable/classes/class_upnp.html) to deal with this.