title: Attach invoice PDF in invoice email
body: <p>I am trying to find a way to attach the default invoice Pdf file in the invoice Mail. 
  I've found some tryouts on this issue but nothing of them worked. </p>
  
  <p>Currently i tried this tutorial: <a href="http://www.ericpan.com/2013/02/14/add-pdf-attachment-to-invoice-email/#.VOS44Xa6ab4" rel="nofollow">http://www.ericpan.com/2013/02/14/add-pdf-attachment-to-invoice-email/#.VOS44Xa6ab4</a></p>
  
  <p>Do you have any ideas regarding this ? </p>