Provide TLS-enabling configuration with stunnel or similar

[sternenseemann]

Recently it seems to be a trend to TLS-enable gopher servers and even some gopher clients seem to support TLS. I don't think it's a good idea to support it in spacecookie, since it is a non-standard feature, but it seems like a good idea to figure out, how TLS typically is set up for gopher and provide an stunnel (?) based example configuration for TLS with spacecookie.

The best way to set up an encrypted spacecookie remains to use a hidden service (but we should close #13 for that).