generated man pages: use xorg footer and no hard coded extension

generated man pages: use xorg footer and no hard coded extension

The section number is no longer hard-coded
The left footer is now "X Version 11".
The center footer is the package name with the version, "libxcb 1.9"
The three values above are provided through xorg-macros. They are passed-in
to the python c_client code.

Example of footer (last line, above dotted line)

[...]
AUTHOR
       Generated from xproto.xml. Contact xcb@lists.freedesktop.org for cor‐
       rections and improvements.

X Version 11                      libxcb 1.9                 xcb_send_event(3)

------------------------------------------------------------------------------

Reviewed-by: Josh Triplett <josh@joshtriplett.org>
Signed-off-by: Gaetan Nadon <memsize@videotron.ca>