Chat adapter for Discord

[nmohoric]

I believe this would require work in the following repos:

operable/cog
operable/piper
operable/go-relay (?)
operable/greenbar

Possibly others.

[rebyn]

For reference, vanstee wrote a short guide here: https://github.com/operable/cog-book/blob/e8b42e84b8e67143ec83eeb5b7ae112fe51b7bb3/src/reference/chat_adapter_interface.adoc