migrate openmcl-devel mailing list away from Mailman

[xrme]

The list openmcl-devel@clozure.com is hosted by Mailman 2.1.39. Mailman 2 needs Python 2, which is obsolete.

One possible alternative might be mlmmj (this is what the FreeBSD project did for all of their Mailman-hosts mailing lists).

Hosting mailing lists is a pain generally. Gmail and other places like gmx.de are becoming hard to deliver to: they sometimes throttle mailing list traffic, want SPF/DMARC/DKIM records, and so forth. But I still think a mailing list is a valuable tool.