增加从参数中取RESTFUL数值的功能

[afengsoft]

    app().registerHandler(
    "/user/{user-name}",
    [](const HttpRequestPtr &req,
       std::function<void(const HttpResponsePtr &)> &&callback,
       const std::string &name) {

       auto username = req->getParameter("user-name");//可以这样取值
        auto resp = HttpResponse::newHttpResponse();
        resp->setBody("Hello, " + name + "!");
        callback(resp);
    },
    {Get});