Initialize dart-lang/tuple with the tuple package at v1.0.1.

lib/tuple.dart

+// Copyright (c) 2014, the tuple 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.
+
+/// # Tuple data structure
+///
+/// - [Tuple2], [Tuple3]...
+///
+/// ## Usage example
+///
+/// ```dart
+/// const t = const Tuple2<String, int>('a', 10);
+///
+/// print(t.item1); // prints 'a'
+/// print(t.item2); // prints '10'
+/// ```
+///
+/// ```dart
+/// const t1 = const Tuple2<String, int>('a', 10);
+/// final t2 = t1.withItem1('c');
+/// // t2 is a new [Tuple2] object with item1 is 'c' and item2 is 10.
+/// ```
+library tuple;
+
+import 'package:quiver_hashcode/hashcode.dart';
+
+part 'package:tuple/src/tuple.dart';