title: os.listdir analog for a zipped directory
body: <p>My goal is to list all files contained in the certain <strong>sub</strong>-directory inside a zip-archive.</p>
  
  <p><code>os.listdir(target_dir)</code> raises a <code>FileNotFoundError</code>, and <code>zfile.namelist()</code> just lists all the files in all directories. </p>
  
  <p>Any ideas?</p>