Switch to openstackdocstheme 2.2.1 and reno 3.1.0 versions. Using
these versions 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: Ifff5d0860f0c9e68a0187242335c5bf7c383a486
Update docs building:
* Switch to sphinx-build
* Update requirements for Sphinx and openstackdocstheme for
python 3, create doc/requiremetns
* Remove unneeded doc and translation sections from setup.cfg
* Remove install_command, it's unneeded, the default is fine.
* Move constraints to deps, use TOX_CONSTRAINTS instead of obsolete
UPPER_CONSTRAINTS
* Remove now unneeded placeholder file
Change-Id: I649e6fa86c17262698cc8a01d042a87b020239d9