filters: add matching against attachment filename

The mimetype of attachments are set by the sender, which can results in
attachments getting not so useful mimetypes (e.g.
application/octet-stream for a csv). Allow matching filter against
filenames directly, by adding the `.filename,` and `.filename,~` syntax,
similarly to headers.

Changelog-added: Match filters on filename via `.filename,~<regexp> =`.
Signed-off-by: Bence Ferdinandy <bence@ferdinandy.com>
Acked-by: Robin Jarry <robin@jarry.cc>

0 files changed, 0 insertions, 0 deletions