Native paddle button support#156

Tons of controllers these days have paddle buttons on the back, but to use them you need to bind them to another button using the steam overlay, which especially sucks in tournament situations.

It’d be sick if we could bind the paddle buttons in-game so we don’t have to do the awkward, “hey can i just open steam to do the paddles, oops, wait which controller is mine, oh no i think i messed yours up sorry” before every tournament set.