Move examples to //sky/sdk/example

sky/sdk/example/game/lib/node_with_size.dart

 part of sprites;
 
 /// The super class of any [Node] that has a size.
 ///
 /// NodeWithSize adds the ability for a node to have a size and a pivot point.
 abstract class NodeWithSize extends Node {
 
   /// Changing the size will affect the size of the rendering of the node.
   ///
   ///     myNode.size = new Size(1024.0, 1024.0);
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   bool isPointInside (Point nodePoint) {
 
     double minX = -size.width * pivot.x;
     double minY = -size.height * pivot.y;
     double maxX = minX + size.width;
     double maxY = minY + size.height;
     return (nodePoint.x >= minX && nodePoint.x < maxX &&
             nodePoint.y >= minY && nodePoint.y < maxY);
   }
 }