code: function renderDirectory(cwd, dir, res){
    var content = '';
    content += '<h1>Index of '+ dir.replace(cwd, '') +'</h1>';
    content += '<hr />';
    fs.readdir(dir, function(err, files){
      content += '<table width="50%">';
      content += '<tr>';
      content += '<td><a href="..">../</a></td>';
      content += '</tr>';
      files.map(function(filename){
        var stat = fs.statSync(path.join(dir, filename));
        filename = filename +  (stat.isDirectory() ? '/' : '');
        content += '<tr>';
        content += '<td><a href="' + filename + '">' + filename + '</a></td>';
        content += '<td>' + (stat.mtime || '-')      +                '</td>';
        content += '<td>' + (stat.size        )      +                '</td>';
        content += '</tr>';
      }).join('');
      content += '</table>';
      content += '<hr/>';
      content += 'Powered by <a href="https://github.com/song940/kelp-static" >kelp-static</a>';
      res.setHeader('Content-Type', 'text/html');
      res.end(content);
    });
  }
docs: [renderDirectory description]
  @param  {[type]}   dir      [description]
  @param  {Function} callback [description]
  @return {[type]}            [description]