title: Generate filename with creation date
body: <p>I'm using dompdf to create and mail a PDF file to my mail and at the same time, save a .txt version on the server.
  Saving the file is working as it should, but im having a bit of trouble getting it to save it with a unique name. In this case i wanted something like date-time.txt ( 06-09-2012_11:43.txt )</p>
  
  <p>or even better, if it could have the name from the text field "refnr" as the name.</p>
  
  <pre><code>&lt;label for="refnr"&gt;&lt;b&gt;Referensnummer:&lt;/b&gt;&lt;/label&gt;
  &lt;input type="text" name="refnr" id="refnr" class="input" /&gt;
  </code></pre>
  
  <p>The code looks like this: </p>
  
  <pre><code>$html = '/html.php';
  $filename = $dir.'/Admin/files/"date here".txt';
  $dompdf = new DOMPDF(); 
  $dompdf-&gt;load_html($html); 
  $dompdf-&gt;set_paper('a4', 'portrait');
  $dompdf-&gt;render(); 
  file_put_contents($filename, $dompdf-&gt;output()); 
  </code></pre>
  
  <p>I tried to play around with <code>$name='myfile_'.date('m-d-Y_hia)';</code> but couldn't make that work, it just gave an error on that line every time.
  So now im here to seek the guidance from you smart people :)</p>