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/battle/check_battle_scene.asm

@@ -0,0 +1,47 @@
+CheckBattleScene: ; 4ea44
+; Return carry if battle scene is turned off.
+
+	ld a, BANK(wLinkMode)
+	ld hl, wLinkMode
+	call GetFarWRAMByte
+	cp LINK_MOBILE
+	jr z, .mobile
+
+	ld a, [wOptions]
+	bit BATTLE_SCENE, a
+	jr nz, .off
+
+	and a
+	ret
+
+.mobile
+	ld a, [wcd2f]
+	and a
+	jr nz, .from_wram
+
+	ld a, 4 ; MBC30 bank used by JP Crystal; inaccessible by MBC3
+	call GetSRAMBank
+	ld a, [$a60c] ; address of MBC30 bank
+	ld c, a
+	call CloseSRAM
+
+	ld a, c
+	bit 0, c
+	jr z, .off
+
+	and a
+	ret
+
+.from_wram
+	ld a, BANK(w5_dc00)
+	ld hl, w5_dc00
+	call GetFarWRAMByte
+	bit 0, a
+	jr z, .off
+
+	and a
+	ret
+
+.off
+	scf
+	ret