Performs the BFG9000's attack from the Doom press-release beta version. Each call of the function fires two plasma projectiles, one is green and the other is red, with a slight random spread. The BFG calls this function 40 times costing 40 points of ammunition with 1-tic interval between each call.
This simulates said Doom version's BFG9000's firing sequence.
Fire: BFGG A 10 A_BFGSound BFGG BBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBBB 1 A_FireOldBFG BFGG B 0 A_Light0 BFGG B 20 A_ReFire Goto Ready