Add Clone for Listener

src/lib.rs

@@ -169,3 +169,12 @@ impl<'a> Future for Listen<'a> {
         Poll::Pending
     }
 }
+
+impl Clone for Listener {
+    fn clone(&self) -> Self {
+        Self {
+            id: None,
+            state: Arc::clone(&self.state),
+        }
+    }
+}