Add tokio-buf and a BufStream trait (#611)

The `BufStream` trait provides an improved API for working with
asynchronous streams of bytes compared to `Stream<Item = [u8]>`

tokio-buf/src/lib.rs

@@ -0,0 +1,20 @@
+#![doc(html_root_url = "https://docs.rs/tokio-buf/0.1.0")]
+#![deny(missing_docs, missing_debug_implementations)]
+#![cfg_attr(test, deny(warnings))]
+
+//! Asynchronous stream of bytes.
+//!
+//! This crate contains the `BufStream` trait and a number of combinators for
+//! this trait. The trait is similar to `Stream` in the `futures` library, but
+//! instead of yielding arbitrary values, it only yields types that implement
+//! `Buf` (i.e, byte collections).
+
+extern crate bytes;
+extern crate either;
+#[macro_use]
+extern crate futures;
+
+pub mod buf_stream;
+
+#[doc(inline)]
+pub use buf_stream::BufStream;