Migrate to using tokio-io

Deprecate the existing `io` module in this crate entirely.

More details coming soon!

Closes #61

src/channel.rs

@@ -5,6 +5,7 @@
 
 #![deprecated(since = "0.1.1", note = "use `futures::sync::mpsc` instead")]
 #![allow(deprecated)]
+#![cfg(feature = "with-deprecated")]
 
 use std::io;
 use std::sync::mpsc::TryRecvError;
@@ -95,6 +96,10 @@ impl<T> Sink for Sender<T> {
     fn poll_complete(&mut self) -> Poll<(), io::Error> {
         Ok(().into())
     }
+
+    fn close(&mut self) -> Poll<(), io::Error> {
+        Ok(().into())
+    }
 }
 
 impl<T> Clone for Sender<T> {