support mouse wheel

0110-on.mouse_wheel_move

@@ -0,0 +1,30 @@
+on.mouse_wheel_move = function(dx, dy)
+	if App.shift_down() then
+		-- shift+scroll wheel doesn't set dx for me; manually do so if necessary
+		if dx == 0 then
+			dx,dy = dy,dx
+		end
+	end
+	if dy > 0 then
+		for i = 1,math.floor(dy) do
+			Viewport.y = Viewport.y - scale(200)
+		end
+		B()
+	elseif dy < 0 then
+		for i = 1,math.floor(-dy) do
+			Viewport.y = Viewport.y + scale(200)
+		end
+		B()
+	end
+	if dx > 0 then
+		for i = 1,math.floor(dx) do
+			Viewport.x = Viewport.x - scale(500)
+		end
+		B()
+	elseif dx < 0 then
+		for i = 1,math.floor(-dx) do
+			Viewport.x = Viewport.x + scale(500)
+		end
+		B()
+	end
+end