object oriented Authentication-Results headers

 Mail::AuthenticationResults provides a parser which copes with most styles of
 Authentication-Results header seen in the wild, but is not yet fully RFC7601
 compliant
 .
 Differences from RFC7601
 .
 key/value pairs are parsed when present in the authserv-id section, this is
 against RFC but has been seen in headers added by Yahoo!.
 .
 Comments added between key/value pairs will be added after them in the data
 structures and when stringified.