add SHR 80boxes spiral transition

res/SFX.CONF

@@ -44,6 +44,7 @@ SHR.80BOXES
 SHR.FIZZLE
 SHR.TWOPASS.LR
 SHR.DIAGONAL
+SHR.80.SPIRAL
 SHR.LR
 SHR.FADEIN
 SHR.LR2

src/fx/fx.shr.80boxes.spiral.a

@@ -0,0 +1,28 @@
+;license:MIT
+;(c) 2021 by 4am
+;
+
+!cpu 6502
+!to "build/FX.INDEXED/SHR.80.SPIRAL",plain
+*=$A000
+
+         !source "src/fx/fx.shr.80boxes.common.a"
+
+         !byte $E9,$E8,$E7,$E6,$E5,$E4,$E3,$E2,$E1,$00
+         !byte $EA,$CF,$CE,$CD,$CC,$CB,$CA,$C9,$E0,$FF
+         !byte $EB,$D0,$BD,$BC,$BB,$BA,$B9,$C8,$DF,$FE
+         !byte $EC,$D1,$BE,$B3,$B2,$B1,$B8,$C7,$DE,$FD
+         !byte $ED,$D2,$BF,$B4,$B5,$B6,$B7,$C6,$DD,$FC
+         !byte $EE,$D3,$C0,$C1,$C2,$C3,$C4,$C5,$DC,$FB
+         !byte $EF,$D4,$D5,$D6,$D7,$D8,$D9,$DA,$DB,$FA
+         !byte $F0,$F1,$F2,$F3,$F4,$F5,$F6,$F7,$F8,$F9
+
+StageInitialIndexes
+         !byte 7,0,0,0,0,0,0
+         !byte 6,0,0,0,0,0,0
+         !byte 5,0,0,0,0,0,0
+         !byte 4,0,0,0,0,0,0
+         !byte 3,0,0,0,0,0,0
+         !byte 2,0,0,0,0,0,0
+         !byte 1
+EndStageInitialIndexes