allow configuration of separator for various suffix formats, mostly used by OJS

dcd.pl

@@ -374,7 +374,9 @@ sub get_all_urls
 sub split_doi_string
 {
   my $doi= shift;  # e.g. 10.25365/phaidra.1
-  my $id_separator= shift || '.';
+  my $id_separator= shift;
+  
+  $id_separator= qr(\.) if (!$id_separator || $id_separator eq '.');
 
   my ($pfx, $sfx)= split ('/', $doi, 2);
   my ($ns, $nr)= split ($id_separator, $sfx, 2);