Add subdirectories to engine/ similar to pokecrystal

engine/battle/move_effects/recoil.asm

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+RecoilEffect_:
+	ld a, [H_WHOSETURN]
+	and a
+	ld a, [wPlayerMoveNum]
+	ld hl, wBattleMonMaxHP
+	jr z, .recoilEffect
+	ld a, [wEnemyMoveNum]
+	ld hl, wEnemyMonMaxHP
+.recoilEffect
+	ld d, a
+	ld a, [wDamage]
+	ld b, a
+	ld a, [wDamage + 1]
+	ld c, a
+	srl b
+	rr c
+	ld a, d
+	cp STRUGGLE ; struggle deals 50% recoil damage
+	jr z, .gotRecoilDamage
+	srl b
+	rr c
+.gotRecoilDamage
+	ld a, b
+	or c
+	jr nz, .updateHP
+	inc c ; minimum recoil damage is 1
+.updateHP
+; subtract HP from user due to the recoil damage
+	ld a, [hli]
+	ld [wHPBarMaxHP+1], a
+	ld a, [hl]
+	ld [wHPBarMaxHP], a
+	push bc
+	ld bc, wBattleMonHP - wBattleMonMaxHP
+	add hl, bc
+	pop bc
+	ld a, [hl]
+	ld [wHPBarOldHP], a
+	sub c
+	ld [hld], a
+	ld [wHPBarNewHP], a
+	ld a, [hl]
+	ld [wHPBarOldHP+1], a
+	sbc b
+	ld [hl], a
+	ld [wHPBarNewHP+1], a
+	jr nc, .getHPBarCoords
+; if recoil damage is higher than the Pokemon's HP, set its HP to 0
+	xor a
+	ld [hli], a
+	ld [hl], a
+	ld hl, wHPBarNewHP
+	ld [hli], a
+	ld [hl], a
+.getHPBarCoords
+	coord hl, 10, 9
+	ld a, [H_WHOSETURN]
+	and a
+	ld a, $1
+	jr z, .updateHPBar
+	coord hl, 2, 2
+	xor a
+.updateHPBar
+	ld [wHPBarType], a
+	predef UpdateHPBar2
+	ld hl, HitWithRecoilText
+	jp PrintText
+HitWithRecoilText:
+	TX_FAR _HitWithRecoilText
+	db "@"