build xdg-shell feature since it's disabled by default

Since xdg-shell is not a stable feature
it should be enabled at runtime using env variable.

See 6d12d9839 which introduces OZONE_WAYLAND_USE_XDG_SHELL

Signed-off-by: Philippe Coval <philippe.coval@open.eurogiciel.org>
ignore backup files

Signed-off-by: Philippe Coval <philippe.coval@open.eurogiciel.org>
Add myself to the AUTHORS file as requested

Signed-off-by: Philippe Coval <philippe.coval@open.eurogiciel.org>