Trac #34740: dead hyperlinks in developer manual

The following section of the developer manual:

https://doc.sagemath.org/html/en/developer/sage_manuals.html

contains multiple reference to a dead link:

http://sphinx.pocoo.org

URL: https://trac.sagemath.org/34740
Reported by: gh-DavidAyotte
Ticket author(s): David Ayotte
Reviewer(s): Kwankyu Lee

build/pkgs/configure/checksums.ini

@@ -1,4 +1,4 @@
 tarball=configure-VERSION.tar.gz
-sha1=013bfce4d1d0d0d68553c4025647445b7036f4db
-md5=a429cd9c90d6bd90f7b2254b7fed8669
-cksum=1487098037
+sha1=e0181bbac24005f264d3b3c5458ff93e75ea0f41
+md5=2f6a6be6f7607c6483cf8dd1fc94da7a
+cksum=2354327490

build/pkgs/configure/package-version.txt

@@ -1 +1 @@
-03f68f4aa9602d246824f764e2ea328fa52577c7
+2cb4c13e573102053b045da783a4799f9a14717c

src/doc/en/developer/sage_manuals.rst

@@ -8,7 +8,7 @@ The Sage Manuals
 
 Sage's manuals are written in `ReST <http://docutils.sourceforge.net/rst.html>`_
 (reStructuredText), and generated with the software `Sphinx
-<http://sphinx.pocoo.org>`_:
+<https://www.sphinx-doc.org/>`_:
 
 .. LIST-TABLE::
  :widths: 4 12
@@ -84,7 +84,7 @@ The documentation can contain links toward modules, classes, or methods, e.g.::
 
 For links toward classes, methods, or function, replace **:mod:** by
 **:class:**, **:meth:** or **:func:** respectively. See `Sphinx' documentation
-<http://sphinx.pocoo.org/markup/inline.html>`_.
+<https://www.sphinx-doc.org/en/master/usage/restructuredtext/roles.html>`_.
 
 **Short links:** the link ``:func:`~sage.mod1.mod2.mod3.func1``` is equivalent
 to ``:func:`func1 <sage.mod1.mod2.mod3.func1>```: the function's name will be
@@ -195,7 +195,7 @@ Two **help** commands which give plenty of documentation for the ``sage
  sage --docbuild -H # a more comprehensive one
 
 **Output formats:** All output formats supported by Sphinx (e.g. pdf) can be
-used in Sage. See `<http://sphinx.pocoo.org/builders.html>`_.
+used in Sage. See `<http://www.sphinx-doc.org/builders.html>`_.
 
 **Broken links:** in order to build the documentation while reporting the broken
 links that it contains, use the ``--warn-links`` flag. Note that Sphinx will not