build+docs: switch to python3, refresh FAQ and INSTALL documents

Refs: #5095
Change-Id: Icdc0e9463b28c07783edbe392a9bc47136947e3b
diff --git a/docs/conf.py b/docs/conf.py
index 60dd74f..f95dbcd 100644
--- a/docs/conf.py
+++ b/docs/conf.py
@@ -12,7 +12,7 @@
 # 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 os
+# import os
 import sys
 # sys.path.insert(0, os.path.abspath('.'))
 
@@ -20,7 +20,7 @@
 # -- Project information -----------------------------------------------------
 
 project = u'Named Data Networking Forwarding Daemon (NFD)'
-copyright = u'Copyright © 2014-2019 Named Data Networking Project.'
+copyright = u'Copyright © 2014-2020 Named Data Networking Project.'
 author = u'Named Data Networking Project'
 
 # The short X.Y version
@@ -58,12 +58,7 @@
         sys.stderr.write("Extension '%s' not found. "
                          "Some documentation may not build correctly.\n" % extension)
 
-if sys.version_info[0] >= 3:
-    addExtensionIfExists('sphinxcontrib.doxylink')
-
-# sphinxcontrib.googleanalytics is currently not working with the latest version of Sphinx
-# if os.getenv('GOOGLE_ANALYTICS', None):
-#     addExtensionIfExists('sphinxcontrib.googleanalytics')
+addExtensionIfExists('sphinxcontrib.doxylink')
 
 # The master toctree document.
 master_doc = 'index'
@@ -156,7 +151,3 @@
 extlinks = {
     'issue': ('https://redmine.named-data.net/issues/%s', 'issue #'),
 }
-
-if os.getenv('GOOGLE_ANALYTICS', None):
-    googleanalytics_id = os.environ['GOOGLE_ANALYTICS']
-    googleanalytics_enabled = True