Updating peewee class fields via dictionary
Rather than implementing this as a part of peewee, feel free to subclass `Model` and implement it yourself.

Feature request.

In Python, you can update object fields via `self.__dict__.update(dictionary)` - this saves a lot of code when reading in data from text files.

Peewee object fields can't be updated in this way, so it would be nice with a convenience method that let you hand a dictionary to a Model object, and have the object fields updated accordingly. 
