Split codec code (#128)

* move src/codec.rs -> src/codec/mod.rs
* Move traits Encoder and Decoder from src/framed_{read|write}.rs into src/codec/{encoder,decoder}.rs
* Move LinesCodec and BytesCodec from src/codecs.rs into src/codec/{lines,bytes}_codec.rs

tokio-io/src/framed.rs

@@ -2,8 +2,9 @@ use std::io::{self, Read, Write};
 use std::fmt;
 
 use {AsyncRead, AsyncWrite};
-use framed_read::{framed_read2, framed_read2_with_buffer, FramedRead2, Decoder};
-use framed_write::{framed_write2, framed_write2_with_buffer, FramedWrite2, Encoder};
+use codec::{Decoder, Encoder};
+use framed_read::{framed_read2, framed_read2_with_buffer, FramedRead2};
+use framed_write::{framed_write2, framed_write2_with_buffer, FramedWrite2};
 
 use futures::{Stream, Sink, StartSend, Poll};
 use bytes::{BytesMut};
@@ -225,4 +226,4 @@ pub struct FramedParts<T>
     pub readbuf: BytesMut,
     /// A buffer with unprocessed data which are not written yet.
     pub writebuf: BytesMut
-}
+}