ldoc doesn't allow to specify fields from class "A" into class "B",
so the only solution is to merge the 2.
Also, one of the most common complain on IRC since Awesome 3.0 is
that the client API doc is confusing since it is in 2 different files.
Also restore the `awful.client` doc link, point to `client`
This will avoid broken links.
Emmanuel Lepage Vallee