Raise errors instead of using asserts

[thijstriemstra]

For example for https://github.com/rm-hull/max7219/blob/master/max7219/led.py#L46:

if cascaded <= 0:
    raise ValueError("Must have at least one device! Got {0}".format(
        cascaded))

[rm-hull]

Closing this issue as it relates to the older deprecated version of the code