Streaming support

[tonyhb]

Implements websocket streaming for channels and the streaming spec

	stream, err := streaming.Subscribe(ctx, jwt)
	if err != nil {
		return fmt.Errorf("error subscribing: %w", err)
	}

	// stream is automatically closed when ctx is done, so this will stop
	// polling and blocking automatically.
	for msg := range stream {
		switch msg.Kind() {
		case streaming.StreamMessage:
			// Handle message
		case streaming.StreamChunk:
			// Handle chunk
		}

	}