Restructure the yaml package.

pkg/yaml/lib/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.
 
 /// A parser for [YAML](http://www.yaml.org/).
 ///
 /// Use [loadYaml] to load a single document, or [loadYamlStream] to load a
 /// stream of documents. For example:
 ///
 ///     import 'package:yaml/yaml.dart';
 ///     main() {
 ///       var doc = loadYaml("YAML: YAML Ain't Markup Language");
 ///       print(doc['YAML']);
 ///     }
 ///
 /// This library currently doesn't support dumping to YAML. You should use
 /// `stringify` from `dart:json` instead:
 ///
 ///     import 'dart:json' as json;
 ///     import 'package:yaml/yaml.dart';
 ///     main() {
 ///       var doc = loadYaml("YAML: YAML Ain't Markup Language");
 ///       print(json.stringify(doc));
 ///     }
 library yaml;
 
-import 'dart:math' as Math;
-import 'dart:collection' show Queue;
+import 'src/composer.dart';
+import 'src/constructor.dart';
+import 'src/parser.dart';
+import 'src/yaml_exception.dart';
 
-import 'deep_equals.dart';
-
-part 'yaml_map.dart';
-part 'model.dart';
-part 'parser.dart';
-part 'visitor.dart';
-part 'composer.dart';
-part 'constructor.dart';
+export 'src/yaml_exception.dart';
+export 'src/yaml_map.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.
+/// are [YamlMap]s. 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.
+/// are [YamlMap]s. 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()
-      .map((doc) => new _Constructor(new _Composer(doc).compose()).construct())
+  return new Parser(yaml).l_yamlStream()
+      .map((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;
-}