docs/sphinx: Refresh config for newer Sphinx

Sphinx 5.0 and newer objects to language = None.  Switch to 'en'.

Also update the copyright year.  Use %Y to avoid this problem in the future,
and provide compatibility for versions of Sphinx prior to 8.1 which don't
support the syntax.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>

docs/conf.py

@@ -3,9 +3,8 @@
 #
 # Configuration file for the Sphinx documentation builder.
 #
-# This file does only contain a selection of the most common options. For a
-# full list see the documentation:
-# http://www.sphinx-doc.org/en/master/config
+# For the full list of built-in configuration values, see the documentation:
+# https://www.sphinx-doc.org/en/master/usage/configuration.html
 
 # -- Path setup --------------------------------------------------------------
 
@@ -19,11 +18,18 @@
 
 
 # -- Project information -----------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#project-information
+
+import sphinx
 
 project = u'Xen'
-copyright = u'2019, The Xen development community'
+copyright = u'2019-%Y, The Xen development community'
 author = u'The Xen development community'
 
+if sphinx.version_info < (8, 1):
+    from datetime import datetime
+    copyright = datetime.today().strftime(copyright)
+
 # Pull the Xen version straight out of the Makefile
 try:
     xen_ver = xen_subver = xen_extra = None
@@ -45,6 +51,7 @@ finally:
         version = release = u"unknown version"
 
 # -- General configuration ---------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#general-configuration
 
 # If your documentation needs a minimal Sphinx version, state it here.
 #
@@ -69,10 +76,7 @@ master_doc = 'index'
 
 # The language for content autogenerated by Sphinx. Refer to documentation
 # for a list of supported languages.
-#
-# This is also used if you do content translation via gettext catalogs.
-# Usually you set "language" from the command line for these cases.
-language = None
+language = 'en'
 
 # List of patterns, relative to source directory, that match files and
 # directories to ignore when looking for source files.
@@ -86,6 +90,7 @@ primary_domain = 'c'
 highlight_language = 'none'
 
 # -- Options for HTML output -------------------------------------------------
+# https://www.sphinx-doc.org/en/master/usage/configuration.html#options-for-html-output
 
 # The theme to use for HTML and HTML Help pages.  See the documentation for
 # a list of builtin themes.