/**
  * Get a worksheet by title (name)
  * 
  * @param string $title name of the worksheet
  * 
  * @return \Google\Spreadsheet\Worksheet
  */
 public function getByTitle($title)
 {
     foreach ($this->xml->entry as $entry) {
         if ($entry->title->__toString() == $title) {
             $worksheet = new Worksheet($entry);
             $worksheet->setPostUrl($this->getPostUrl());
             return $worksheet;
         }
     }
     return null;
 }