Move sky/examples to sky/sdk/lib/example, and code changes to support that change. Fixes T277.

sky/examples/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 {
-
-  Image _image;
-  Map<String, Texture> _textures = new Map();
-
-  /// Creates a new sprite sheet from an [_image] and a sprite sheet [jsonDefinition].
-  ///
-  ///     var mySpriteSheet = new SpriteSheet(myImage, jsonString);
-  SpriteSheet(this._image, String jsonDefinition) {
-    assert(_image != null);
-    assert(jsonDefinition != null);
-
-    JsonDecoder decoder = new JsonDecoder();
-    Map file = decoder.convert(jsonDefinition);
-    assert(file != null);
-
-    List frames = file["frames"];
-
-    for (Map frameInfo in frames) {
-      String fileName = frameInfo["filename"];
-      Rect frame = _readJsonRect(frameInfo["frame"]);
-      bool rotated = frameInfo["rotated"];
-      bool trimmed = frameInfo["trimmed"];
-      Rect spriteSourceSize = _readJsonRect(frameInfo["spriteSourceSize"]);
-      Size sourceSize = _readJsonSize(frameInfo["sourceSize"]);
-      Point pivot = _readJsonPoint(frameInfo["pivot"]);
-
-      var texture = new Texture._fromSpriteFrame(_image, fileName, sourceSize, rotated, trimmed, frame,
-        spriteSourceSize, pivot);
-      _textures[fileName] = texture;
-    }
-  }
-
-  Rect _readJsonRect(Map data) {
-    num x = data["x"];
-    num y = data["y"];
-    num w = data["w"];
-    num h = data["h"];
-
-    return new Rect.fromLTRB(x.toDouble(), y.toDouble(), (x + w).toDouble(), (y + h).toDouble());
-  }
-
-  Size _readJsonSize(Map data) {
-    num w = data["w"];
-    num h = data["h"];
-
-    return new Size(w.toDouble(), h.toDouble());
-  }
-
-  Point _readJsonPoint(Map data) {
-    num x = data["x"];
-    num y = data["y"];
-
-    return new Point(x.toDouble(), y.toDouble());
-  }
-
-  /// 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];
-}