$0158E8 - Given ID and bitfield's offset, checks if the given chest has been opened
	Returns 0x01 if it has, 0x00 if not	
	-Also used for other bitfields!

$05C4C0 - Chest opening routine
$05C594 - When opening a chest, determines if you can carry any more of the given item
	$807EFBC - Gets quantity of the item

$05C834
	$05C90E - When opening a chest, this routine sets the "opened" flag