Ensure QR codes have a border large enough (#235)

*  Ensure QR codes have a border large enough
(The QR code spec requires a border at least 4*box_size thick but we can't
 just set border=16 because that results in a QR code more than 255px tall
 and I'm not yet ready to use fullimage() as a backend for it)
This fix was originally commited by Stephan Sokolow on 2014-05-22
* Let the user print stuff using qr example
* fix tests

src/escpos/escpos.py

@@ -211,7 +211,10 @@ class Escpos(object):
             qr_img = qr_code.make_image()
             im = qr_img._img.convert("RGB")
             # Convert the RGB image in printable image
+            self.text('\n')
             self.image(im)
+            self.text('\n')
+            self.text('\n')
             return
         # Native 2D code printing
         cn = b'1'  # Code type for QR code