anchor.diff:    * create an `app/core` folder
     * 创建`app/core`文件夹
     * move the `UserService` and `TitleComponent` from `app/` to `app/core`
  -  * 把`UserService`和`TitleComponent`从`app`移到`app`中
  +  * 把`UserService`和`TitleComponent`从`app`移到`app/core`中
     * create a `CoreModule` class to own the core material
     * 创建一个`CoreModule`类来管理这些核心素材
     * update the `AppRoot` module to  import `CoreModule`
  
positive.code:   
    Again, most of this is familiar blocking and tackling. The interesting part is the `CoreModule`
    
    又只剩下一些熟悉的普通任务了，但这次是针对`CoreModule`的：
    
  +makeExample('ngmodule/ts/app/core/core.module.ts', 'v4', 'app/app/core/core.module.ts')
  
  
negative.code: 
    The last line calls the `forRoot` static class method of the `RouterModule`, passing in the configuration.
    
    最后一行调用了`RouterModule`类的静态方法`forRoot`，并把路由配置信息传给它。
    
  +makeExample('ngmodule/ts/app/app.routing.ts', 'forRoot')(format='.')
  
  