perlootut: replace Object::Tiny with Class::Tiny

Class::Tiny is similarly small and simple in API, but with more powerful
features available.  Comparison to Object::Tiny and Class::Accessor is
here: https://metacpan.org/pod/Class::Tiny#RATIONALE

At mst's suggestion, a link to Class::Tiny::Antlers for Moose-syntax
is included.