PKAV and FWKCS #603

I have reverse engineered PKAV (including reading the otherwise encrypted AVEXTRA data) that is used with a lot of archives - see https://github.com/johnsonjh/pkstuff#authenticity-verification and my implementation for it I added to Info-ZIP ZIP and UnZIP at https://github.com/johnsonjh/infozip-av#pkav-and-fwkcs-for-infozip

While of course this is mostly useful for historical archives, might this be something you'd be interested in supporting?

There are actually many older archives that include these signatures and often include useful information in the AVDATA text.

Likewise support for FWKCS (MD5), while MD5 is also obsolete, it beats CRC-32 if that's what an archive has.