This commit adds a unix socket on which you can receive internal events
as they happen. Currently the only supported event is a chat message
being added. Intended for external applications that depend on chat
messages, e.g. text-to-speech or Twitch Plays Pokémon.
Also implements stack/queue behaviour where if the eyes limit would be
exceeded, either the new eyes cause the oldest eyes to be deleted OR
the new eyes aren't created at all. The default is the first option.
n9k