Highlight deprecated features

Highlight deprecated features

We have quite a list of deprecated options currently.  Ensure this
is highlighted both in documentation and code.

This patch builds on the wiki page [1] enlisting all deprecated features
and their status.  There are also some options not listed here, as
there exists patches in release/2.4 which awaits an update for git master.

[1] https://community.openvpn.net/openvpn/wiki/DeprecatedOptions

Signed-off-by: David Sommerseth <davids@openvpn.net>
Acked-by: Steffan Karger <steffan@karger.me>
Message-Id: <20170815215451.21662-1-davids@openvpn.net>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg15261.html
Signed-off-by: David Sommerseth <davids@openvpn.net>