message: feat(body): replace the `Payload` trait with `HttpBody`
  The `hyper::body::HttpBody` trait is a re-export from the `http-body`
  crate. This allows libraries to accept "HTTP bodies" without needing to
  depend on hyper.
  BREAKING CHANGE: All usage of `hyper::body::Payload` should be replaced
  with `hyper::body::HttpBody`.
diff: //!
  //! There are two pieces to this in hyper:
  //!
  -//! - The [`Payload`](body::Payload) trait the describes all possible bodies. hyper
  -//! allows any body type that implements `Payload`, allowing applications to
  -//! have fine-grained control over their streaming.
  -//! - The [`Body`](Body) concrete type, which is an implementation of `Payload`,
  -//! and returned by hyper as a "receive stream" (so, for server requests and
  -//! client responses). It is also a decent default implementation if you don't
  -//! have very custom needs of your send streams.
  -
  -#[doc(hidden)]
  +//! - The [`HttpBody`](body::HttpBody) trait the describes all possible bodies.
  +//! hyper allows any body type that implements `HttpBody`, allowing
  +//! applications to have fine-grained control over their streaming.
  +//! - The [`Body`](Body) concrete type, which is an implementation of
  +//! `HttpBody`, and returned by hyper as a "receive stream" (so, for server
  +//! requests and client responses). It is also a decent default implementation
  +//! if you don't have very custom needs of your send streams.
  +
  pub use http_body::Body as HttpBody;
  pub use self::body::{Body, Sender};
  pub use self::chunk::Chunk;
  -pub use self::payload::Payload;
  +pub(crate) use self::payload::Payload;
  mod body;
  mod chunk;
  