Improved Auto-Fire

Auto-Fire has been made much more useful, instead of a set fire-rate it calculates based on your bullet limit how fast it can fire to keep a steady rhythm, so the longer you live and the more kills you score you can go from a steady stream to a river of death.

Fixed a bug where additional enemy ships for CoOp/Solo mode always spawn in the blue zone even if they are orange.
Improved the particle explosion logic to be more resource efficient, runs noticeably better on weaker machines now.