Move examples to //sky/sdk/example

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

 part of sprites;
 
 /// A sprite sheet packs a number of smaller images into a single large image.
 ///
 /// The placement of the smaller images are defined by a json file. The larger image and json file is typically created
 /// by a tool such as TexturePacker. The [SpriteSheet] class will take a reference to a larger image and a json string.
 /// From the image and the string the [SpriteSheet] creates a number of [Texture] objects. The names of the frames in
 /// the sprite sheet definition are used to reference the different textures.
 class SpriteSheet {
 
@@ skipping 54 matching lines @@
   /// The image used by the sprite sheet.
   ///
   ///     var spriteSheetImage = mySpriteSheet.image;
   Image get image => _image;
 
   /// Returns a texture by its name.
   ///
   ///     var myTexture = mySpriteSheet["example.png"];
   Texture operator [](String fileName) => _textures[fileName];
 }