.. 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.

The gettext_compact can now be a string which is then a single domain
for all documents.

Fixes #784

Since python3.5, subprocess.run() has been introduced. It works a
wrapper of Popen, and it looks much simple and better. This uses it
instead of Popen to make our code simple.