Reverse wheel scroll axis on shift pressed

Resolve #548.

src/js/plugin/handler/mouse-wheel.js

@@ -52,6 +52,10 @@ function bindMouseWheelHandler(element, i) {
       deltaY = e.wheelDelta;
     }
 
+    if (e.shiftKey) {
+      // reverse axis with shift key
+      return [-deltaY, -deltaX];
+    }
     return [deltaX, deltaY];
   }