Consuming app builder pattern

[ynuwenhof]

Use the consuming builder pattern to make the construction of apps more intuitive.

New

let app = App::<Request, Ctx, ()>::new_basic().get("/plaintext", m![plaintext]);

let server = Server::new(app);
server.start("0.0.0.0", 4321);

Old

    let mut app = App::<Request, Ctx, ()>::new_basic();
    app.get("/plaintext", m![plaintext]);

    let server = Server::new(app);
    server.start("0.0.0.0", 4321);