Charpacks a given bitmap
It is possible to continue a charpacking by supporting a tuple of
a character list and a screen as the second parameter.
:param bitmap: the c64 bitmap to charpack
:param ret: optional charpack result for continuing
Loads an image file, charpacks it, saves the obtained screen and character
set and shows the original image, its bitmap representation, and the charpacking
= _Feature((2, 6, 0, 'alpha', 2), (3, 0, 0, 'alpha', 0), 65536)