Asyncronously read from client and broadcast to others.

echo server example (run in terminal):
  - start the service
  php 007_broadcast_server.php

  - Connect to 127.0.0.1 at port 1337 from various terminals;
  nc 127.0.0.1 1337

  - Type in anything and press ENTER; Reactor will asyncronously read
    from client and broadcast to others.