Buttons and changed keys

I’ve added a sample image which wasn’t backgroundless like I’d hoped
but oh well we’ll change the icon anyway. The icons go transparent when
pressed and then refill. I also changed the up and down keys to w and
s, and the three buttons work with the z, x and c keys as suggested.
Also I made the margins of how far the ship can go a little bit shorter
as I noticed you could still go so far off-screen that the bullets
would stop firing. Anything else looking odd or that I haven’t
commented just message me :)