simplify the api

[fisadev]

The current API requires you to instantiate a class, set attributes, call methods and then watch the side effect reading other attributes. That's a lot of innecesary complexity for a library that could simply be:

def create_qr(data, redundancy_level, pixel_size):
    return an image object (so you can save it or do whatever you want)

def read_qr(image_object):
    return a string with the readed data (or None if unable to read)

You should watch this video (a python core developer on the last pycon), and will understand why you shouldn't use classes and side effects in this case:
http://pyvideo.org/video/880/stop-writing-classes

I'll work on a patch if you agree.