codec: change Encoder to take &Item (#1746)

Co-authored-by: Markus Westerlind <[email protected]>

examples/chat.rs

@@ -193,9 +193,7 @@ async fn process(
     let mut lines = Framed::new(stream, LinesCodec::new());
 
     // Send a prompt to the client to enter their username.
-    lines
-        .send(String::from("Please enter your username:"))
-        .await?;
+    lines.send("Please enter your username:").await?;
 
     // Read the first line from the `LineCodec` stream to get the username.
     let username = match lines.next().await {
@@ -232,7 +230,7 @@ async fn process(
             // A message was received from a peer. Send it to the
             // current user.
             Ok(Message::Received(msg)) => {
-                peer.lines.send(msg).await?;
+                peer.lines.send(&msg).await?;
             }
             Err(e) => {
                 println!(