Mirror texture horizontally, inverting each pixel on the X axis

Property definitions

gamnit $ Sprite :: invert_x=
	# Mirror `texture` horizontally, inverting each pixel on the X axis
	fun invert_x=(value: Bool)
	do
		if isset _invert_x and value != invert_x then needs_update
		invert_x_direct = value
	end
lib/gamnit/flat/flat_core.nit:168,2--173,4