Add more equery options
_gentoo_packages, _portage: Added sets completion

Signed-off-by: Vadim A. Misbakh-Soloviov <mva@mva.name>
_gentoo_packages, _portage: reworked sets completion, added portage options

Signed-off-by: Vadim A. Misbakh-Soloviov <mva@mva.name>