Prevent default on wheel events -- keeps page from scrolling (#408)

hxd/Stage.js.hx

@@ -192,6 +192,7 @@ class Stage {
 	}
 
 	function onMouseWheel(e:js.html.WheelEvent) {
+		e.preventDefault();
 		var ev = new Event(EWheel, mouseX, mouseY);
 		ev.wheelDelta = e.deltaY / 120; // browser specific?
 		event(ev);
@@ -251,4 +252,4 @@ class Stage {
 		event(ev);
 	}
 
-}
+}