title: argparse.print_help() ArgumentParser message string
body: <p>I am writing a slack bot, and I am using <code>argsparse</code> to parse the arguments sent into the slackbot, but I am trying to figure out how to get the help message string so I can send it back to the user via the slack bot. </p>
  
  <p>I know that <code>ArgumentParser</code> has a <code>print_help()</code> method, but that is printed via console and I need a way to get that string.</p>