feat: move mblog header handling into mime4cl r/3754

Accessing the headers of a MIME message feels like something mime4cl
should handle. We implemented this ad hoc in mblog before in order to
not need to worry about doing it in a sensible way. Now we introduce a
decent-ish interface for getting a header from a MIME message,
mime-message-header-values:

* It returns a list because MIME message headers may appear multiple
  times.

* It decodes RFC2047 only upon request, as you may want to be stricter
  about parsing certain fields.

* It checks header name equality case insensitively.

The code for decoding the RFC2047 string is retained and still uses
babel for doing the actual decoding.

Change-Id: I58bbbe4b46dbded04160b481a28a40d14775673d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/5150
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

0 files changed, 0 insertions, 0 deletions