Module info

I just figured out that there is already a fix for uniq values (sort_field),
but it has a bug, due to List::MoreUtils::uniq.

    my $fixer = Catmandu::Fix->new(
        fixes => ["uniq('values')"]
    );
    print Dumper(
        $fixer->fix({
            values => [undef,"a"]
        })
    );

Reason: List::MoreUtils tries to insert "undef" as key in a hash, which is prohibited.

See Catmandu::Fix::uniq in this branch for the fix