title: How to broadcast a message from a Phoenix Controller to a Channel?
body: <p>Is there a way to broadcast a message to a channel from outside that channel?</p>
  
  <p>Maybe something like <code>Channel.broadcast topic, event, data</code>?</p>
  
  <p>I saw something like this <a href="https://github.com/phoenixframework/phoenix/issues/70">here</a> but the final version of <code>Phoenix.Channel.broadcast/3</code> (as of today) takes a socket which implies the channel and topic.</p>