title: slack rtm api, get usernames from dm channel id and vice-versa
body: <p>I'm playing around with the <a href="https://api.slack.com/rtm" rel="nofollow">slack rtm api</a>, and they say that "You can send a message to a private group or direct message channel in the same way, but using a Group ID (C024BE91L) or DM channel ID (D024BE91L)." Is there any way to get from the DM channel ID to the username that you are sending the direct message to?</p>