how to make a handlers' group?

Sometimes we need to organize multiple handlers into a group, they have the same URL prefix, and there may be global middleware in the group. Context::makeGroup() can help us with this feature.

void GroupGlobalMiddleWare(vogro::Context & ctx) {
    ctx.response->addBody("hello from group global handler<br>");
    ctx.Next();
}

void TestHandler1(vogro::Context& ctx) {
    ctx.response->addBody("hello from handler1<br>");
    ctx.Next();
}

void TestHandler2(vogro::Context& ctx) {
    ctx.response->addBody("hello from handler2<br>");
    ctx.Next();
}

void TestHandler3(vogro::Context& ctx) {
    ctx.response->addBody("hello from handler3<br>");
}

void PostHandler(vogro::Context & ctx) {
    ctx.response->addBody("post");
}

void PutHandler(vogro::Context & ctx) {
    ctx.response->addBody("put");
}

void DeleteHandler(vogro::Context & ctx) {
    ctx.response->addBody("delete");
}

auto userGroup = server.makeGroup("/group", GroupGlobalMiddleWare);
{
    userGroup->Get("/get", TestHandler1, TestHandler2, TestHandler3);
    userGroup->Post("/post", PostHandler);
    userGroup->Put("/put", PutHandler);
    userGroup->Delete("/delete", DeleteHandler);
}

/group/get/ --> GroupGlobalMiddleWare --> TestHandler1 --> TestHandler2 --> TestHandler3

/group/post/ --> GroupGlobalMiddleWare --> PostHandler

/group/put/ --> GroupGlobalMiddleWare --> PutHandler

/group/delete/ --> GroupGlobalMiddleWare --> DeleteHandler