L::Path: Overload some operators

Signed-off-by: Niels Thykier <niels@thykier.net>
L::C::Package: Have sorted_*index return L::Path objects

Have sorted_index (etc.) return a list of L::Path objects instead of
just strings.  With this patch:

   for my $file ($info->sorted_index) {
       my $path = $info->index($file);
       ...
   }

Can be reduced to:

   for my $path ($info->sorted_index) {
       ...
   }

Signed-off-by: Niels Thykier <niels@thykier.net>