Matrix support #451

Emulsion should optionally support Matrix on the same principles as Telegram and XMPP.

Implementation Notes

A new messaging protocol requires two main things:

• MessageSenderContext:

  emulsion/Emulsion.Messaging/MessageSender.fs

  Lines 13 to 17 in 715bce9

  	type MessageSenderContext = {
  	Send: OutgoingMessage -> Async<unit>
  	Logger: ILogger
  	RestartCooldown: TimeSpan
  	}

  (essentially one function)

• an implementation of IMessageSystem:

  emulsion/Emulsion.Messaging/MessageSystem.fs

  Lines 14 to 21 in 715bce9

  	/// The IM message queue. Manages the underlying connection, reconnects when necessary, stores the outgoing messages in
  	/// a queue and sends them when possible. Redirects the incoming messages to a function passed when starting the queue.
  	type IMessageSystem =
  	/// Starts the IM connection, manages reconnects. Never terminates unless cancelled.
  	abstract member RunSynchronously : IncomingMessageReceiver -> unit
  	/// Queues the message to be sent to the IM system when possible.
  	abstract member PutMessage : OutgoingMessage -> unit

  or MessageSystemBase:

  emulsion/Emulsion.Messaging/MessageSystem.fs

  Line 46 in 715bce9

  type MessageSystemBase(ctx: ServiceContext, cancellationToken: CancellationToken) as this =

  (essentialy three functions — Send, RunUntilError, RunAsync, I barely remember why there are two Runs, but perhaps this is connected with some wacky Telegram bot interaction protocol; we have the docs though!)

• message "muxer" is already implemented in the MessagingCore:

  emulsion/Emulsion/MessagingCore.fs

  Line 17 in 715bce9

  type MessagingCore(

  It will need to be adjusted for three message types.

• message "demuxer" is kinda available as MessageSender:

  emulsion/Emulsion.Messaging/MessageSender.fs

  Line 66 in 715bce9

  let internal receiver (ctx: MessageSenderContext) (inbox: Sender): Async<unit> =

  — it uses persistent queue and sending retry. No need to adjust that, an implementation of aforementioned MessageSenderContext will be enough.,