New port: mail/s-nail

S-nail provides a simple and friendly environment for sending and
receiving mail. It is intended to provide the functionality of the
POSIX mailx(1) command, but is MIME capable and optionally offers
extensions for line editing, S/MIME, SMTP and POP3, among others.
S-nail divides incoming mail into its constituent messages and allows
the user to deal with them in any order. It offers many COMMANDS and
INTERNAL VARIABLES for manipulating messages and sending mail. It
provides the user simple editing capabilities to ease the composition
of outgoing messages, and increasingly powerful and reliable
non-interactive scripting capabilities.

WWW: https://www.sdaoden.eu/code.html#s-mailx

PR: 232189
Submitted by: Yasuhiro KIMURA <yasu@utahime.org>
Approved by: mentors (implicit)