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

lib/core/double.dart

 // Copyright (c) 2011, 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.
 
 // Dart core library.
 
 interface double extends num {
   static final double NAN = 0.0 / 0.0;
   static final double INFINITY = 1.0 / 0.0;
   static final double NEGATIVE_INFINITY = -INFINITY;
 
   // Specialization of super-interface. Double is contagious. We can therefore
   // specialize more methods than in other num sub-interfaces.
   double remainder(num other);
   double operator +(num other);
   double operator -(num other);
   double operator *(num other);
   double operator %(num other);
   double operator /(num other);
   double operator ~/(num other);
   double operator negate();
   double abs();
   double round();
   double floor();
   double ceil();
   double truncate();
 }