hack to set the adequate settings module based on which project doc is built),
activate extlinks extension for swh-web and add links to swh projects dedicated doc
on the index page but also a link to the swh urls index

Build prior to swh.web module.  It's a workaround the time to find a
more sustainable solution.

Related T763

Django wants to know the path to its configuration file at import time, which is
somewhat annoying when using autodoc on a Django project such as swh.web.

Close T763.

Works around T763 until a generic solution is found