Burst fire for some projectile weapons

Added two new vars for all guns, burst_size and fire_delay.
Burst_size will loop the firing code however many times you set the var to. Fire_delay controls how much time between each shot is fired in the burst.
This PR is coinciding with my semi-nerf to some ballistic weapons here (https://github.com/tgstation/-tg-station/pull/6293) by making them deal stamina damage instead of stunning, because it will require multiple hits to stun. This makes it easier so you don't have to spam dose clikks as a nuke op. I figured I would separate these two PRs though because people might want the burst fire but not the ranged stun nerfs.

Finally removed the comment at the top of automatic.dm :')