* canonical_root setting is the path to the root of the canonical sphinx doc,
if not set no canonical link is generated, must end with "/"
* canonical_branch defines the canonical branch to which to redirect, defaults
to master
also various side-fixes:
* disabled permalinks in sphinx instead of hiding them via CSS
* improved generation of github links, removed _app global and setting of
linkcode_resolve in conf.py
Xavier Morel