Node.traverse() was marked as deprecated since docutils-0.18.  Instead
of it, Node.findall() has been added as successor of traverse().

This applies a patch to docutils-0.17 or older to be available
Node.findall() and use it.

Since 0.18, Element.traverse() returns an iterator instead of
intermediate object.  As a result, the return value is always considered
as truthy value.  And it becomes fragile when the caller modifies the
doctree on the loop.

.. note::

   $ find sphinx tests LICENSE doc/conf.py -type f -exec sed -i '' -e 's/2007\-20../2007-2021/' {} \;
   $ git co sphinx/locale/**/*.js sphinx/templates/epub3/mimetype

Keep imports alphabetically sorted and their order homogeneous across
Python source files.

The isort project has more feature and is more active than the
flake8-import-order plugin.

Most issues caught were simply import ordering from the same module.
Where imports were purposefully placed out of order, tag with
isort:skip.

To control trimming doctest flags manually, this adds new options
:trim-doctest-flags: and :no-trim-doctest-flags: to doctest
directives.  It helps to describes doctest module itself in python
doc (see #6698).

Apply PEP 526 based variable annotation style to namedtuples.  It
is available since python 3.6.