Update conf.py from git tag, fix sphinx warnings (#5716)

Fixes #5671

Implements https://protips.readthedocs.io/git-tag-version.html

Fix a myriad of minor Sphinx warnings generated in the docs.

doc/conf.py

@@ -16,6 +16,7 @@
 # add these directories to sys.path here. If the directory is relative to the
 # documentation root, use os.path.abspath to make it absolute, like shown here.
 #
+import re
 import os
 import sys
 # sys.path.insert(0, os.path.abspath('.'))
@@ -55,10 +56,10 @@ author = u'Ivan Grokhotkov'
 # |version| and |release|, also used in various other places throughout the
 # built documents.
 #
+# Tip from https://protips.readthedocs.io/git-tag-version.html to get version from tag
+release = re.sub('^v', '', os.popen('git describe').read().strip())
 # The short X.Y version.
-version = u'2.5.0-beta3'
-# The full version, including alpha/beta/rc tags.
-release = u'2.5.0-beta3'
+version = release
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.