Change capture docs to use namedtuple

doc/en/capture.rst

@@ -94,12 +94,12 @@ an example test function that performs some output related checks:
     def test_myoutput(capsys): # or use "capfd" for fd-level
         print("hello")
         sys.stderr.write("world\n")
-        out, err = capsys.readouterr()
+        captured = capsys.readouterr()
-        assert out == "hello\n"
+        assert captured.out == "hello\n"
-        assert err == "world\n"
+        assert captured.err == "world\n"
         print("next")
-        out, err = capsys.readouterr()
+        captured = capsys.readouterr()
-        assert out == "next\n"
+        assert captured.out == "next\n"
 
 The ``readouterr()`` call snapshots the output so far -
 and capturing will be continued.  After the test
@@ -117,6 +117,10 @@ system level output streams (FD1 and FD2).
 
 .. versionadded:: 3.3
 
+The return value from ``readouterr`` changed to a ``namedtuple`` with two attributes, ``out`` and ``err``.
+
+.. versionadded:: 3.3
+
 If the code under test writes non-textual data, you can capture this using
 the ``capsysbinary`` fixture which instead returns ``bytes`` from
 the ``readouterr`` method.  The ``capfsysbinary`` fixture is currently only