add onSelected callback to KissExtendedSprite

src/kiss_flixel/DragToSelectPlugin.hx

@@ -109,6 +109,11 @@ class DragToSelectPlugin extends FlxBasic {
                                 }
                             }
                         }
+                        for (s in dragState.selectedSprites) {
+                            if (s.onSelected != null) {
+                                s.onSelected();
+                            }
+                        }
                     } else if (!rect.isEmpty) {
                         dragState.debugLayer.drawFlxRect(rect);
                     }

src/kiss_flixel/KissExtendedSprite.hx

@@ -138,6 +138,8 @@ class KissExtendedSprite extends flixel.addons.display.FlxExtendedSprite {
         }
     }
 
+    public var onSelected:Void->Void = null;
+
     public function pixelPerfectDrag() {
         return _dragPixelPerfect;
     }