Helpful gubbins for iguana-based themes.
Set the default feed to Atom, remove the ability to view non-Atom feeds, add link[rel="alternate"] to head for the feed.
Add the following to app/di.php:
$registrar->addInstance(\Dxw\Iguana\Extras\UseAtom::class, new \Dxw\Iguana\Extras\UseAtom());