Added __version__ to flask__peewee

I was wondering which version of the flask_peewee I was using. Unfortunately, doing the following got me an error:

    >>> import flask_peewee
    >>> print flask_peewee.__version__
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    AttributeError: 'module' object has no attribute '__version__'

So I added __version__ in init.py so that users can more easily track the status of the software they are using. I couldn't find any tags so far, so please note that I set the status to '0.1-dev', but this can of course be anything else.