asio kcp代码走读

（1）kcp_client_wrap类

a 供给办法接口以下：

    send_msg
        kcp_client_.send_msg(msg);
    stop //期待工作线程退出
    set_event_callback
    
    connect //main函数中调用connect进行kcp client的初始化
        kcp_client_.connect_async
        do_asio_kcp_connect_loop    
        
    connect_async
    connect_result    s