Update fixnum to new package guidelines.

pkg/fixnum/intx.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.
-
-part of fixnum;
-
-/**
- * A fixed-precision integer.
- */
-abstract class intx implements Comparable {
-
-  // Arithmetic operations.
-  intx operator +(other);
-  intx operator -(other);
-  // The unary '-' operator.  Note that -MIN_VALUE will be equal
-  // to MIN_VALUE due to overflow.
-  intx operator -();
-  intx operator *(other);
-  intx operator %(other);
-  // Truncating division.
-  intx operator ~/(other);
-  intx remainder(other);
-
-  // Note: no / operator
-
-  // Bit-operations.
-  intx operator &(other);
-  intx operator |(other);
-  intx operator ^(other);
-  intx operator ~();
-  intx operator <<(int shiftAmount);
-  intx operator >>(int shiftAmount);
-  intx shiftRightUnsigned(int shiftAmount);
-
-  // Relational operations, may be applied to intx or int.
-  int compareTo(Comparable other);
-  bool operator ==(other);
-  bool operator <(other);
-  bool operator <=(other);
-  bool operator >(other);
-  bool operator >=(other);
-
-  // Testers.
-  bool get isEven;
-  bool get isMaxValue;
-  bool get isMinValue;
-  bool get isNegative;
-  bool get isOdd;
-  bool get isZero;
-
-  int get hashCode;
-
-  intx abs();
-
-  /**
-   * Returns the number of leading zeros in this [intx] as an [int]
-   * between 0 and 64.
-   */
-  int numberOfLeadingZeros();
-
-  /**
-   * Returns the number of trailing zeros in this [intx] as an [int]
-   * between 0 and 64.
-   */
-  int numberOfTrailingZeros();
-
-  /**
-   * Converts this [intx] to a [List] of [int], starting with the least
-   * significant byte.
-   */
-  List<int> toBytes();
-
-  /**
-   * Converts this [intx] to an [int].  On some platforms, inputs with large
-   * absolute values (i.e., > 2^52) may lose some of their low bits.
-   */
-  int toInt();
-
-  /**
-   * Converts an [intx] to 32 bits.  Narrower values are sign extended and
-   * wider values have their high bits truncated.
-   */
-  int32 toInt32();
-
-  /**
-   * Converts an [intx] to 64 bits.
-   */
-  int64 toInt64();
-
-  /**
-   * Returns the value of this [intx] as a decimal [String].
-   */
-  String toString();
-
-  /**
-   * Returns the value of this [intx] as a hexadecimal [String].
-   */
-  String toHexString();
-
-  /**
-   * Returns the value of this [intx] as a [String] in the given radix.
-   * [radix] must be an integer between 2 and 16, inclusive.
-   */
-  String toRadixString(int radix);
-}