Monster spawner

Spawn shooters shoot skull cubes that spawn monsters (and can telefrag, killing anything on the landing spot, even a player with god mode on). When you are up against a spawner (which does not always have Romero's head with it, but usually does), you will hear this backwards "To win the game you must kill me, John Romero" and it sounds like "grrrrrr reh ooh seye, j'imbre selfetiay dombrin deus".

The monsters land at spawn spots placed around the map. The spawn spots are used in rotation, in the order they are defined in the THINGS lump in the WAD file. If there are no spawn spots, the spawn shooter still makes its wakeup sound but never shoots any cubes.

Monster list:
 * Imp
 * Demon
 * Spectre
 * Cacodemon
 * Hell Knight
 * Baron of Hell
 * Mancubus
 * Arachnotron
 * Revenant
 * Pain Elemental
 * Arch-Vile