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

corelib/src/num.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.
-
-abstract class num implements Comparable, Hashable {
-  factory num._uninstantiable() {
-    throw const UnsupportedOperationException(
-        "abstract class num cannot be instantiated");
-  }
-  // Arithmetic operations.
-  abstract num operator +(num other);
-  abstract num operator -(num other);
-  abstract num operator *(num other);
-  abstract num operator %(num other);
-  abstract double operator /(num other);
-  // Truncating division.
-  abstract num operator ~/(num other);
-  // The unary '-' operator.
-  abstract num operator negate();
-  abstract num remainder(num other);
-
-  // Relational operations.
-  abstract bool operator <(num other);
-  abstract bool operator <=(num other);
-  abstract bool operator >(num other);
-  abstract bool operator >=(num other);
-
-  // Predicates.
-  abstract bool isNaN();
-  abstract bool isNegative();
-  abstract bool isInfinite();
-
-  abstract num abs();
-  abstract num round();
-  abstract num floor();
-  abstract num ceil();
-  abstract num truncate();
-
-  abstract int toInt();
-  abstract double toDouble();
-
-  abstract String toStringAsFixed(int fractionDigits);
-  abstract String toStringAsExponential(int fractionDigits);
-  abstract String toStringAsPrecision(int precision);
-  abstract String toRadixString(int radix);
-}