Update #18 - The Shooter

[p]New Runner Shooter enemy - keeps distance, fires fast green Firebolts, harder to kill, appears from Mission #5[/p]
[p]Multiple Shooters per mission - expect crossfire and flanks[/p]
[p]New player spawn locations - better map variety and early flow[/p]
[p]AI spawner improvements - tighter control of timing, distance, and mix[/p]
[p]Chem Gun - performance pass and a counting bug fix[/p]
[p]Fireball optimization - lighter tick, improved hit handling[/p]