Port to Sphinx 8.0 (#349)

The old `intersphinx_mapping` format has been removed; it must now map
identifiers to (target, inventory) tuples.

Author: cjwatson

doc/conf.py

@@ -196,6 +196,6 @@
 
 
 # Example configuration for intersphinx: refer to the Python standard library.
-intersphinx_mapping = {'http://docs.python.org/': None}
+intersphinx_mapping = {'python': ('http://docs.python.org/', None)}
 
 autoclass_content="both"