Wishlist: add option --base64url to cksum (in addition to --base64)

[Denis Excoffier]

Hello,
Please add to cksum the option --base64url like --base64 added recently 
(release 9.2, 2023-03-20).
Indeed, tr ‘+/‘ ‘-_’ is not an easy option (‘tr’ applies to filename) even if 
stdin is used (filename is ‘-‘).
Of course, basenc also works great to produce the same (using e.g. cksum -a 
sha1 --raw).
Regards,
Denis Excoffier.