Implement Clone for Sink combinators where it makes sense

Author: rubdos

src/sink/from_err.rs

@@ -5,7 +5,7 @@ use {Sink, Poll, StartSend};
 /// A sink combinator to change the error type of a sink.
 ///
 /// This is created by the `Sink::from_err` method.
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 #[must_use = "futures do nothing unless polled"]
 pub struct SinkFromErr<S, E> {
     sink: S,

src/sink/map_err.rs

@@ -3,7 +3,7 @@ use sink::Sink;
 use {Poll, StartSend, Stream};
 
 /// Sink for the `Sink::sink_map_err` combinator.
-#[derive(Debug)]
+#[derive(Clone,Debug)]
 #[must_use = "sinks do nothing unless polled"]
 pub struct SinkMapErr<S, F> {
     sink: S,

src/sink/with.rs

@@ -7,7 +7,7 @@ use stream::Stream;
 
 /// Sink for the `Sink::with` combinator, chaining a computation to run *prior*
 /// to pushing a value into the underlying sink.
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 #[must_use = "sinks do nothing unless polled"]
 pub struct With<S, U, F, Fut>
     where S: Sink,
@@ -20,7 +20,7 @@ pub struct With<S, U, F, Fut>
     _phantom: PhantomData<fn(U)>,
 }
 
-#[derive(Debug)]
+#[derive(Clone, Debug)]
 enum State<Fut, T> {
     Empty,
     Process(Fut),