ngircd: Add optional SSL / TLS support

Unfortunately, irssi doesn't have a command-line flag to select
encrypted connections [1].  I'd like something like:

  $ irssi -c irc.example.net -p 6697 --ssl

Until something like that is added, you'll need to add the server to
your irssi config:

  $ cat ~/.irssi/config
  ...
  servers = (
    {
      address = "irc.example.net";
      chatnet = "example";
      port = "6697";
      use_ssl = "yes";
      ssl_verify = "yes";
      autoconnect = "yes";
    },
    ...
  );
  chatnets = {
    example = {
      type = "IRC";
      nick = "your-nick";
    };
    ...
  };
  ...

Or connect manually after firing up irssi:

  $ irssi --noconnect
  [(status)] /connect -ssl -ssl_verify nott 6697

Run `/help connect` for more information.

[1]: http://www.irssi.org/documentation/manual