Create tokio-codec (#360)

Create a new tokio-codec crate with many of the contents of
`tokio_io::codec`.

tokio-io/src/codec/bytes_codec.rs

@@ -1,9 +1,12 @@
+#![allow(deprecated)]
+
 use bytes::{Bytes, BufMut, BytesMut};
 use codec::{Encoder, Decoder};
 use std::io;
 
 /// A simple `Codec` implementation that just ships bytes around.
 #[derive(Copy, Clone, Debug, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[deprecated(since = "0.1.7", note = "Moved to tokio-codec")]
 pub struct BytesCodec(());
 
 impl BytesCodec {