Switch to newer openstackdocstheme and reno versions

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.

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.

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.

See also
http://lists.openstack.org/pipermail/openstack-discuss/2020-May/014971.html

Change-Id: I3b5249bee4f8452cc3a717dc93d2eca70002ce59

doc/requirements.txt

@@ -2,5 +2,5 @@
 # of appearance. Changing the order has an impact on the overall integration
 # process, which may cause wedges in the gate later.
 
-sphinx>=1.8.0,!=2.1.0 # BSD
-openstackdocstheme>=1.20.0 # Apache-2.0
+sphinx>=2.0.0,!=2.1.0 # BSD
+openstackdocstheme>=2.2.1 # Apache-2.0

doc/source/conf.py

@@ -78,9 +78,9 @@ source_suffix = '.rst'
 master_doc = 'index'
 
 # openstackdocstheme options
-repository_name = 'openstack/python-aodhclient'
-bug_project = 'python-aodhclient'
-bug_tag = ''
+openstackdocs_repo_name = 'openstack/python-aodhclient'
+openstackdocs_bug_project = 'python-aodhclient'
+openstackdocs_bug_tag = ''
 copyright = u'2015, OpenStack Foundation'
 
 # If true, '()' will be appended to :func: etc. cross-reference text.
@@ -91,7 +91,7 @@ add_function_parentheses = True
 add_module_names = True
 
 # The name of the Pygments (syntax highlighting) style to use.
-pygments_style = 'sphinx'
+pygments_style = 'native'
 
 # -- Options for HTML output --------------------------------------------------
 

releasenotes/source/conf.py

@@ -52,9 +52,9 @@ source_suffix = '.rst'
 master_doc = 'index'
 
 # openstackdocstheme options
-repository_name = 'openstack/python-aodhclient'
-bug_project = 'python-aodhclient'
-bug_tag = ''
+openstackdocs_repo_name = 'openstack/python-aodhclient'
+openstackdocs_bug_project = 'python-aodhclient'
+openstackdocs_bug_tag = ''
 copyright = u'2015-present, Aodh developers'
 
 # Release notes are version independent.
@@ -93,7 +93,7 @@ exclude_patterns = []
 # show_authors = False
 
 # The name of the Pygments (syntax highlighting) style to use.
-pygments_style = 'sphinx'
+pygments_style = 'native'
 
 # A list of ignored prefixes for module index sorting.
 # modindex_common_prefix = []