cargo fmt (#604)

Run rustfmt and setup CI to check for it.

examples/async_stream.rs

@@ -1,18 +1,11 @@
 #![deny(warnings)]
 
-#[macro_use]
-extern crate futures;
-extern crate bytes;
-extern crate reqwest;
-extern crate tokio;
-extern crate tokio_threadpool;
-
 use std::io::{self, Cursor};
 use std::mem;
 use std::path::Path;
 
 use bytes::Bytes;
-use futures::{Async, Future, Poll, Stream};
+use futures::{try_ready, Async, Future, Poll, Stream};
 use reqwest::r#async::{Client, Decoder};
 use tokio::fs::File;
 use tokio::io::AsyncRead;