Replace HTTP links with HTTPS ones: documentation

Rationale:
Reduces attack surface on kernel devs opening the links for MITM
as HTTPS traffic is much harder to manipulate.

Deterministic algorithm:
For each file:
  For each line:
    If doesn't contain `\bxmlns\b`:
      For each link, `\bhttp://[^# \t\r\n]*(?:\w|/)`:
        If both the HTTP and HTTPS versions
        return 200 OK and serve the same content:
          Replace HTTP with HTTPS.

Signed-off-by: Alexander A. Klimov <grandmaster@al2klimov.de>
Link: https://lore.kernel.org/r/20200526060544.25127-1-grandmaster@al2klimov.de
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/conf.py

@@ -538,7 +538,7 @@ epub_exclude_files = ['search.html']
 # Grouping the document tree into PDF files. List of tuples
 # (source start file, target name, title, author, options).
 #
-# See the Sphinx chapter of http://ralsina.me/static/manual.pdf
+# See the Sphinx chapter of https://ralsina.me/static/manual.pdf
 #
 # FIXME: Do not add the index file here; the result will be too big. Adding
 # multiple PDF files here actually tries to get the cross-referencing right