docs: def stop(opts, bot, event):
      """Usage: stop [--name=<name>] [--notify=<slack_username>]
  
      Stop a timer.
  
      _name_ works the same as for `start`.
      If given _slack_username_, reply with an at-mention to the given user.
      """
  
      name = opts['--name']
      slack_username = opts['--notify']
  
      now = datetime.datetime.now()
      delta = now - bot.timers.pop(name)
  
      response = bot.stop_fmt.format(delta)
  
      if slack_username:
          mention = ''
  
          # The slack api (provided by https://github.com/os/slacker) is available on all bots.
          users = bot.slack.users.list().body['members']
          for user in users:
              if user['name'] == slack_username:
                  mention = "<@%s>" % user['id']
                  break
          response = "%s: %s" % (mention, response)
  
      return response