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

sky/sdk/lib/example/rendering/borders.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:math' as math;
 import 'dart:sky' as sky;
 
 import 'package:sky/rendering/block.dart';
 import 'package:sky/rendering/box.dart';
 import 'package:sky/rendering/sky_binding.dart';
@@ skipping 57 matching lines @@
         child: new RenderDecoratedBox(
           decoration: new BoxDecoration(
             backgroundColor: new sky.Color(0xFFFFFF00)
           )
         )
       )
     ),
   ]);
   new SkyBinding(root: root);
 }