Headers were built and rebuilt as "Mime-Version" rather than
"MIME-Version". Both are valid per RFC 2045, but some spam filters,
such as rspamd, score the mixed-case form as a deliverability signal.
Fix the header name in the accessor macro and in ParsedHeader's
grammar table, the places that spell it, and update the snapshot
tests across mailparsing, message, kumo-log-types, mod-mimepart, and
kumod that captured the old spelling, along with the reference docs
that showed the old casing in their examples. #564
Augment the docs to clarify that msg:append_header and
msg:prepend_header do no modification of the value by default.
Adjust the wrapping used by Header:new_unstructured so that it
hard wraps before the SMTP line length limit.
Add optional encode parameter to msg:append_header and
msg:prepend_header so that those methods can opt-in to the
Header:new_unstructured formatting.
Add HeaderMap:append method to mirror the existing HeaderMap:prepend
method.
Add unit tests that demonstrate the effect of wrapping/encoding
for both the "dumb" msg:append_header and msg:prepend_header functions,
and the "smarter" HeaderMap:prepend and HeaderMap:append methods that
always encode their parameters.
Update the docs for the headermap flavor of these methods to indicate
that they will always encode the value.
Wez Furlong