[tor-dev] txtorcon support for Twisted 12, 13, 14

I am considering dropping support for Twisted 12, 13 and 14 in the next txtorcon release. Also, TLS support (i.e. pyOpenSSL) will become mandatory as well (that is, the dependency will be on twisted[tls]).

Twisted 12 is only there because of Debian wheezy. Twisted 13 is for wheezy-backports and 14 is for jessie ("stable"). jessie-backports has 16.2.0 and stretch has 16.6.0

Hence I do not believe upgrading this dependency will be a problem for Debian packaging. I do not know the implications for other distributions.

Feedback requested if this will negatively affect you!