* 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
Romain Porte