title: Asynchronous retrieving of access token using twitter4j
body: <p>For now I see that both function of retrieving tokens are
  synchonous(getRequestToken and getAcessToken).</p>
  
  <p>Is it possible to retrieve them asynchronously, and show progress on
  background for example?</p>
  
  <p>P.S. I work under Android platform.</p>
  
  <p>Thanks a lot.</p>