feat(http1): add UpgradeableConnection::into_parts

This allows the connection to be deconstructed into I/O object and
some additional information, provided it hasn't yet been upgraded.

Author: pborzenkov

src/server/conn/http1.rs

@@ -522,6 +522,12 @@ where
             Pin::new(conn).graceful_shutdown()
         }
     }
+
+    /// Return the inner IO object, and additional information provided the connection
+    /// has not yet been upgraded.
+    pub fn into_parts(self) -> Option<Parts<I, S>> {
+        self.inner.map(|conn| conn.into_parts())
+    }
 }
 
 impl<I, B, S> Future for UpgradeableConnection<I, S>