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

sky/sdk/lib/example/rendering/transform.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:sky' as sky;
 
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/flex.dart';
 import 'package:sky/rendering/sky_binding.dart';
 import 'package:vector_math/vector_math.dart';
 
 void main() {
   RenderDecoratedBox green = new RenderDecoratedBox(
     decoration: new BoxDecoration(backgroundColor: const sky.Color(0xFF00FF00))
   );
   RenderConstrainedBox box = new RenderConstrainedBox(
     additionalConstraints: new BoxConstraints.tight(const Size(200.0, 200.0)),
     child: green
   );
 
   Matrix4 transform = new Matrix4.identity();
   RenderTransform spin = new RenderTransform(
       transform: transform, child: box);
   spin.rotateZ(1.0);
 
   RenderFlex flex = new RenderFlex();
   flex.add(spin);
   new SkyBinding(root: flex);
 }