doc: Add stream unzip doc

Author: k-nasa

src/stream/stream/mod.rs

@@ -1719,6 +1719,33 @@ extension_trait! {
             Zip::new(self, other)
         }
 
+        #[doc = r#"
+            Converts an stream of pairs into a pair of containers.
+
+            unzip() consumes an entire stream of pairs, producing two collections: one from the left elements of the pairs, and one from the right elements.
+
+            This function is, in some sense, the opposite of [`zip`].
+
+            [`zip`]: trait.Stream.html#method.zip
+
+            # Example
+
+            ```
+            # fn main() { async_std::task::block_on(async {
+            #
+            use async_std::prelude::*;
+            use async_std::stream;
+
+            let s  = stream::from_iter(vec![(1,2), (3,4)]);
+
+            let (left, right): (Vec<_>, Vec<_>) = s.unzip().await;
+
+            assert_eq!(left, [1, 3]);
+            assert_eq!(right, [2, 4]);
+            #
+            # }) }
+            ```
+        "#]
         #[cfg(feature = "unstable")]
         #[cfg_attr(feature = "docs", doc(cfg(unstable)))]
         fn unzip<A, B, FromA, FromB>(self) -> impl Future<Output = (FromA, FromB)> [UnzipFuture<Self, FromA, FromB>]