Restructure YAML package suitable for pub lish

utils/pub/yaml/yaml.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.
-
-library yaml;
-
-import 'dart:math' as Math;
-import 'dart:collection' show Queue;
-
-import 'deep_equals.dart';
-
-part 'yaml_map.dart';
-part 'model.dart';
-part 'parser.dart';
-part 'visitor.dart';
-part 'composer.dart';
-part 'constructor.dart';
-
-/// Loads a single document from a YAML string. If the string contains more than
-/// one document, this throws an error.
-///
-/// The return value is mostly normal Dart objects. However, since YAML mappings
-/// support some key types that the default Dart map implementation doesn't
-/// (null, NaN, booleans, lists, and maps), all maps in the returned document
-/// are YamlMaps. These have a few small behavioral differences from the default
-/// Map implementation; for details, see the YamlMap class.
-loadYaml(String yaml) {
-  var stream = loadYamlStream(yaml);
-  if (stream.length != 1) {
-    throw new YamlException("Expected 1 document, were ${stream.length}");
-  }
-  return stream[0];
-}
-
-/// Loads a stream of documents from a YAML string.
-///
-/// The return value is mostly normal Dart objects. However, since YAML mappings
-/// support some key types that the default Dart map implementation doesn't
-/// (null, NaN, booleans, lists, and maps), all maps in the returned document
-/// are YamlMaps. These have a few small behavioral differences from the default
-/// Map implementation; for details, see the YamlMap class.
-List loadYamlStream(String yaml) {
-  return new _Parser(yaml).l_yamlStream().mappedBy((doc) =>
-      new _Constructor(new _Composer(doc).compose()).construct())
-      .toList();
-}
-
-/// An error thrown by the YAML processor.
-class YamlException implements Exception {
-  String msg;
-
-  YamlException(this.msg);
-
-  String toString() => msg;
-}