added null filter

h2d/filter/Nothing.hx

@@ -0,0 +1,13 @@
+package h2d.filter;
+
+class Nothing extends Filter {
+
+	public function new() {
+		super();
+	}
+
+	override function draw( ctx : RenderContext, t : h2d.Tile ) {
+		return t;
+	}
+
+}