docs(body): add more docs for Body and Payload

src/lib.rs

@@ -49,8 +49,7 @@ pub use http::{
 
 pub use client::Client;
 pub use error::{Result, Error};
-pub use body::{Body};
-pub use chunk::Chunk;
+pub use body::{Body, Chunk};
 pub use server::Server;
 
 mod common;