docs: attempt to document the general libvirt dev strategy

docs: attempt to document the general libvirt dev strategy

There are various ideas / plans floating around for future libvirt work,
some of which is actively in progress. Historically we've never captured
this kind of information anywhere, except in mailing list discussions.
In particular guidelines in hacking.html.in don't appear until a policy
is actively applied.

This patch attempts to fill the documentation gap, by creating a new
"strategy" page which outlines the general vision for some notable
future changes. The key thing to note is that none of the stuff on this
page is guaranteed, plans may change as new information arises. IOW this
is a "best guess" as to the desired future.

This doc has focused on three areas, related to the topic of language
usage / consolidation

 - Use of non-C languages for the library, daemons or helper tools
 - Replacement of autotools with meson
 - Use of RST and Sphinx for documentation (website + man pages)

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Andrea Bolognani <abologna@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>