code: public function formatHeaders()
  	{
  		$headers = array();
  
  		foreach ($this->headers as $key => $val) {
  			if (is_string($key)) {
  				$headers[] = $key . ': ' . $val;
  			} else {
  				$headers[] = $val;
  			}
  		}
  
  		return $headers;
  	}
docs: Format the headers to an array of 'key: val' which can be passed to
  curl_setopt.
  
  @return array