Introduce boot.js: this finally makes it possible to load and run Todomvc

lib/event.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.
 
 library polymer.event;
 
 import 'dart:html';
-import 'custom_element.dart';
+import 'package:custom_element/custom_element.dart';
 
 /**
  * *Warning*: this is an implementation helper and should not be used in your
  * code. This method will be replaced in favor of calling to the handler
  * via mirrors.
  *
  * Register an event handler.
  */
 void registerEventHandler(String query, void registerEvent(Node node)) {
   if (_eventHandlers == null) {
     _eventHandlers = {};
     CustomElement.templateCreated.add(_hookEvents);
   }
   if (_eventHandlers.containsKey(query)) {
     throw new ArgumentError('duplicate event handler selector $query');
   }
   _eventHandlers[query] = registerEvent;
 }
 
 void _hookEvents(DocumentFragment fragment) {
   _eventHandlers.forEach((query, hookEvent) {
     for (var node in fragment.queryAll(query)) {
       hookEvent(node);
     }
   });
 }
 
 Map<String, Function> _eventHandlers;