build+ci: switch to python3

Also in this commit:
 * Sync CI scripts with other projects
 * Sync sphinx_build waf tool with ndn-cxx
 * Modernize docs/conf.py
 * Replace redmine_issue extension with sphinx.ext.extlinks
 * Fix typo in docs/doxygen.conf.in
 * Improve README.md

Refs: #5095
Change-Id: Iee05500f907442dd7cb3e41bd613beef7461dab4
diff --git a/wscript b/wscript
index 8f95207..6d3946c 100644
--- a/wscript
+++ b/wscript
@@ -142,7 +142,8 @@
         config='docs/conf.py',
         outdir='docs',
         source=bld.path.ant_glob('docs/**/*.rst'),
-        VERSION=VERSION)
+        version=VERSION_BASE,
+        release=VERSION)
 
 def version(ctx):
     # don't execute more than once