Move core and coreimpl from corelib/ to lib/core and lib/coreimpl.

lib/core/object.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /**
  * Everything in Dart is an [Object].
  */
 class Object {
   const Object();
 
   String toString() => ObjectImplementation.toStringImpl(this);
 
   void noSuchMethod(String name, List args) {
     ObjectImplementation.noSuchMethodImpl(this, name, args);
   }
 
   operator ==(other) => this === other;
 
   get dynamic() => this;
 }