Anotate more of the battle anim subsystem

The X and Y flip flags can be applied through the stack consisting of:
- Object attributes
- Animation frame attributes
- OAM Data
Each of these negate eachother.

Confused yet? The same stack is traversed to obtain the final tile ID,
with an added layer on top for the base GFX offset and the offset for
the dynamically loaded GFX requested by the object!

wBattleAnimDelay is populated with the values passed to `anim_wait`.

engine/battle_anims/helpers.asm

@@ -37,16 +37,16 @@ GetBattleAnimFrame:
 	push af
 	ld a, [hl]
 	push hl
-	and $3f
+	and %00111111
 	ld hl, BATTLEANIMSTRUCT_DURATION
 	add hl, bc
 	ld [hl], a
 	pop hl
 .okay
 	ld a, [hl]
-	and $c0
+	and Y_FLIP << 1 | X_FLIP << 1 ; The << 1 is compensated in the "frame" macro
 	srl a
-	ld [wBattleAnimTempAddSubFlags], a
+	ld [wBattleAnimTempFrameOAMFlags], a
 	pop af
 	ret