Add methods to Result. Bump version to 2.0 and remove deprecated features.

test/result/result_test.dart

 // Copyright (c) 2013, 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.
 
 import "dart:async";
 import "dart:collection";
 
 import "package:async/async.dart";
 import "package:stack_trace/stack_trace.dart";
 import "package:test/test.dart";
@@ skipping 338 matching lines @@
   }
 
   static void _nullError(e, StackTrace s) {
     fail("Unexpected sink addError: $e");
   }
 
   static void _nullDone() {
     fail("Unepxected sink close");
   }
 }