Apply async functionality to client library

[barabo]

• swm.sendMessage('customEHR.watchClicks', {...payload}) - handle a stream of responses via generator
• swm.createClient - creates a client object using the messaging handle and target origin
• client.sendMessage('status.handshake') - or any other known types. returns a promise.
• client.sendResponseTo(message) - reads the messageId and sets responseToMessageId
• use new client in app and ehr
• swm.discover() - returns library details

[barabo]

See sketched api here: https://hackmd.io/@jmandel/HyxB7yV9_/edit

[barabo]

FWIW: some of the incorporated async ideas came from this:
https://stackoverflow.com/questions/26150232/resolve-javascript-promise-outside-function-scope

[barabo]

The lib user docs are being tracked in issue #51

[barabo]

To add detail to the remaining desired async functionality, consider this use pattern:

const clicks = client.getMessageResponse("customEHR.watchUserClicks", {...payload});

for await (let click of clicks.generator) { /// async generator syntax... something kinda like this
  console.log("User clicked at", click);
  if (click.x === click.y) {     // because *of course* we're building a y===x detector app...
      clickGenenerator.cancel(); // unregister a promise or generator
                                 // so the client can free up memory
      break; // technically
  }
  console.log("Waiting for another click...")
}

This behavior has not been described by the IG, but it has been discussed as a favorable pattern and specifically encouraged for further experimentation.