sprites: add handgun sights and correct flash perspective; center minigun. (#1118)

Added a rear sight notch.

Made a bigger flash based on the minigun, scaled in proportion to how much space the (imputed) barrel of each weapon view takes up on the screen.

Adjusted the offsets so there isn't quite as much movement with the trigger pull - that weird whole-arm jerk was a mistake from id that we need not emulate, and reducing the movement helps bring out the way the slide actually moves back in the C frame.

Adjusted the shape of the hand so there wasn't that awkward sudden perfectly straight line down the thumb side.

Made the light fade out after each shot instead of just blinking.

Adjusted the minigun's offsets to better center it.

buildcfg.txt

@@ -2185,10 +2185,10 @@ BPAKA0	13	30
 BROKA0	27	20
 CANDA0	8	15
 CBRAA0	14	61
-CHGGA0	-108	-117
-CHGGB0	-108	-121
-CHGFA0	-127	-95
-CHGFB0	-129	-111
+CHGGA0	-107	-117
+CHGGB0	-107	-121
+CHGFA0	-126	-95
+CHGFB0	-128	-111
 CLIPA0	4	12
 COLUA0	9	45
 CSAWA0	22	20
@@ -2219,13 +2219,13 @@ PINSA0	15	39
 PINSB0	15	39
 PINSC0	15	39
 PINSD0	15	39
-PISFA0	-147	-69
-PISGA0	-138	-106
-PISGB0	-138	-88
-PISGC0	-138	-94
-PISGD0	-137	-84		; Unused
-PISGE0	-134	-69		; Unused
-PISTA0	10	14
+PISFA0  -144	-88
+PISGA0  -136	-105
+PISGB0  -136	-101
+PISGC0  -136	-99
+PISGD0  -135	-93		; Unused
+PISGE0  -132	-89		; Unused
+PISTA0	10	15
 PLAYA1	18	54
 PLAYA2A8	11	54
 PLAYA3A7	17	54