Taking inspiration from acme-client.

gemexp is meant for local testing so I'm not too worried about changing its log format if it makes sense to do so.

Using what the manpage advertised. The regress adaptations will follow. The directory will also change (and the key type too.)

don't know what i was smoking when I wrote log_request() like that...

Listening by default on all the addresses is so bad I don't know why I haven't changed this before. Anyway. Add a `listen on $hostname port $port' syntax to the config file and deprecate the old "port" and "ipv6" global setting. Still try to honour them when no "listen on" directive is used for backward compatibily, but this will go away in the next next version hopefully. At the moment the `listen on' in server context don't filter the host, i.e. one can still reach a host from a address not specified in the corresponding `liste on', this will be added later.