Fix snake_case filenames

Renamed a bunch of files, most of them one-off functions, to better fit
the general snake_case naming scheme. Also renamed some awfully long filenames.

engine/gfx/drawkrispackgfx.asm

@@ -1,20 +0,0 @@
-DrawKrisPackGFX: ; 48e81
-	ld hl, PackFGFXPointers
-	add hl, de
-	add hl, de
-	ld a, [hli]
-	ld e, a
-	ld d, [hl]
-	ld hl, vTiles2 tile $50
-	lb bc, BANK(PackFGFX), 15
-	call Request2bpp
-	ret
-
-PackFGFXPointers: ; 48e93
-	dw PackFGFX + (15 tiles) * 1 ; ITEM_POCKET
-	dw PackFGFX + (15 tiles) * 3 ; BALL_POCKET
-	dw PackFGFX + (15 tiles) * 0 ; KEY_ITEM_POCKET
-	dw PackFGFX + (15 tiles) * 2 ; TM_HM_POCKET
-
-PackFGFX: ; 48e9b
-INCBIN "gfx/pack/pack_f.2bpp"