message: docs(server): Example for conn modules
  Add basic, module-level example for the Http struct in the server::conn module that shows how to customize the configuration of the HTTP protocol handling and then serve requests received through a tokio TCP stream.
diff: //!
  //! If you don't have need to manage connections yourself, consider using the
  //! higher-level [Server](super) API.
  +//!
  +//! ## Example
  +//! A simple example that uses the `Http` struct to talk HTTP over a Tokio TCP stream
  +//! ```no_run
  +//! use http::{Request, Response, StatusCode};
  +//! use hyper::{server::conn::Http, service::service_fn, Body};
  +//! use std::{net::SocketAddr, convert::Infallible};
  +//! use tokio::net::TcpListener;
  +//!
  +//! #[tokio::main]
  +//! async fn main() -> Result<(), Box<dyn std::error::Error + Send + Sync>> {
  +//! let addr: SocketAddr = ([127, 0, 0, 1], 8080).into();
  +//!
  +//! let mut tcp_listener = TcpListener::bind(addr).await?;
  +//! loop {
  +//! let (tcp_stream, _) = tcp_listener.accept().await?;
  +//! tokio::task::spawn(async move {
  +//! if let Err(http_err) = Http::new()
  +//! .http1_only(true)
  +//! .keep_alive(true)
  +//! .serve_connection(tcp_stream, service_fn(hello))
  +//! .await {
  +//! eprintln!("Error while serving HTTP connection: {}", http_err);
  +//! }
  +//! });
  +//! }
  +//! }
  +//!
  +//! async fn hello(_req: Request<Body>) -> Result<Response<Body>, Infallible> {
  +//! Ok(Response::new(Body::from("Hello World!")))
  +//! }
  +//! ```
  use std::error::Error as StdError;
  use std::fmt;
  