说明：  专用的功能带来更高的效率，比如我们仅仅处理某几一个网页的显示。我们见过路由里的那个管理路由器的页面吧，那就是一个轻量级的小web server实现，它可放不下一个windows + iis 　　内嵌的windows应用程序，比如我们想在winform里嵌入webBrower，配合它来做一些应用。
(We need to serve HTTP content, to a regular browser, or another HTTP client from our application. Lets create an abstract class for handling the HTTP request, and let the derived class handle the response, without worrying about anything else. )