Adds optional ``headers`` parameter to ``send_mail_plus``. These headers will end up in the header section of the body of the top message, not in any multipart "children" of the message.
1.0.0
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Initial release of stable API
Three utilties are public API:
* ``send_mail_plus`` to handle (inline) attachments * ``sanitize_content`` to strip untrusted/disallowed links from mail content * ``strip_tags_plus`` to convert HTML into a best-effort plain text variant