Get client up to date with the latest server

[mitchellwrosen]

The flow should now be:

• On startup, send a subscribe message.

  { "type": "subscribe", "topic": <room> }
  

• Continue as before with payload messages.

  { "type": "message", "topic": <room>, "payload": <payload> }
  

  The server will forward payload messages whose topic exactly matches any previously subscribed string, without the type tag. They look like:

  { "topic": <room>, "payload": <payload> }