Add Resource package.

lib/resource.dart

 // Copyright (c) 2015, 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 [Resource] is data that can be loaded into a Dart program.
 ///
 /// This library provides an implementation of [Resource] and a
 /// [PackageResolver] that controls how package: URIs are converted to
 /// URIs that can be loaded.
 library resource;
 
 export "src/resource.dart" show Resource, PackageResolver;
+export "src/loader.dart" show ResourceLoader;