`Filter::Util::Call`

The previous version supports ab Ebg13; but not no Rot13;
For that we have to be a little more devious:

        ...
        if ($status >= 0) { 
          if (/^\s*  no  \s+  Rot13  \s*  ; # "no Rot13;"
                \s* (?: #.* )?  $           # Optional WS or comment 
              /x) {
            return $status;
          }
          tr/A-Za-z/N-ZA-Mn-za-m/;
        }
        ...

We examine the line for no Rot13; before we give it to the compiler
If so, we return the line without rot13ing it
We could also have called filter_del() directly
Filter::Simple does this automatically