说明：  C#编写的简易HTTP服务器,能处理GET请求,并发送当前目录内指定的文件,默认文件为"index.htm",找不到文件则发送错误信息 采用多线程编写,能同时连接多个客户端.
(C# summary prepared by the HTTP server can handle GET request, , and send the current directory specified in the document, the default document "index.htm" no documents were sent the wrong message multi-threading, can simultaneously connect to multiple client.)