Doc: do not rely on checked-out Sphinx toolchain from svn.python.org anymore
Nowadays it is likely that people will have Sphinx installed,
and if not, they will know how to install it.
This also simplifies life a lot for distribution packagers,
who typically do not want the doc build process to connect
to external web resources.
diff --git a/Doc/conf.py b/Doc/conf.py
index 5b63cad..69e45de 100644
--- a/Doc/conf.py
+++ b/Doc/conf.py
@@ -61,6 +61,8 @@
# By default, highlight as Python 3.
highlight_language = 'python3'
+needs_sphinx = '1.1'
+
# Options for HTML output
# -----------------------