* 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
Actually the hardware barcode implementation is very specific and not
generic enough for just adding a `soft_render=True` argument to it. This
is a first work that can be improved with other commits, maybe for
merging this method in the `barcode` method after some cleanup.
The width, height and text_distance were set using empiric
print-and-retry tests so that the generated barcode looks nice to the
eye (and to the eye of an Android scanner tool.
!WARNING! Printing a barcode that is too large in width will result in
the printer to go crazy trying to print an image that is too large for
it. This may be fixed by raising an exception in the `image` method.
