Several reorgs:
* setup.cfg/setup.py must be in top-level dir so that siblings
(installing for example openstackdocstheme from source instead of
pip) works.
* Update openstackdocstheme version (see below)
* Remove unused entries from setup.cfg
* Remove py27 code from setup.py
* Update tox.ini for a py3 only world and cleanup
Switch to openstackdocstheme 2.2.1 version. Using
this version will allow especially:
* Linking from HTML to PDF document
* Allow parallel building of documents
* Fix some rendering problems
Update Sphinx version as well.
Disable openstackdocs_auto_name to use 'project' variable as name.
Change pygments_style to 'native' since old theme version always used
'native' and the theme now respects the setting and using 'sphinx' can
lead to some strange rendering.
openstackdocstheme renames some variables, so follow the renames
before the next release removes them. A couple of variables are also
not needed anymore, remove them.
See also
http://lists.openstack.org/pipermail/openstack-discuss/2020-May/014971.html
Change-Id: I27039f9dc52c3e6c9e667b5699172d0f834e8f6b