Enabled unzip_option feature for core tests & unzip docs

library/core/src/option.rs

@@ -1408,6 +1408,8 @@ impl<T, U> Option<(T, U)> {
     /// # Examples
     ///
     /// ```
+    /// #![feature(unzip_option)]
+    ///
     /// let x = Some((1, "hi"));
     /// let y = None::<(u8, u32)>;
     ///

library/core/tests/lib.rs

@@ -66,6 +66,7 @@
 #![feature(slice_group_by)]
 #![feature(trusted_random_access)]
 #![feature(unsize)]
+#![feature(unzip_option)]
 #![deny(unsafe_op_in_unsafe_fn)]
 
 extern crate test;