Rename rendering/render_*.dart to rendering/*.dart

sky/examples/raw/render_paragraph.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';
 import 'package:sky/framework/app.dart';
-import 'package:sky/framework/rendering/render_box.dart';
-import 'package:sky/framework/rendering/render_node.dart';
-import 'package:sky/framework/rendering/render_flex.dart';
-import 'package:sky/framework/rendering/render_paragraph.dart';
+import 'package:sky/framework/rendering/box.dart';
+import 'package:sky/framework/rendering/node.dart';
+import 'package:sky/framework/rendering/flex.dart';
+import 'package:sky/framework/rendering/paragraph.dart';
 
 class RenderSolidColor extends RenderDecoratedBox {
   final Size desiredSize;
   final int backgroundColor;
 
   RenderSolidColor(int backgroundColor, { this.desiredSize: const Size.infinite() })
       : backgroundColor = backgroundColor,
         super(decoration: new BoxDecoration(backgroundColor: backgroundColor));
 
   Size getIntrinsicDimensions(BoxConstraints constraints) {
@@ skipping 35 matching lines @@
 
   child = new RenderDecoratedBox(
     decoration: new BoxDecoration(backgroundColor: 0xFFFFFFFF),
     child: new RenderParagraph(text: meatyString, color: 0xFF009900)
   );
   flexRoot.add(child);
   child.parentData.flex = 1;
 
   app = new AppView(root);
 }