Easy Python 3 compatibility
No, there is _much_ more needed to make Peewee Python 3 compatible. `Model` uses a metaclass, and Python 3 changed how those were defined. Some judicious application of the `six` library would help there.
 I think I'm finally serious about py3 compatibility... I'll start a fix.
 With the release of 2.1.0, peewee's test suite and extra modules are working with 3.2 and 3.3!

This library is nearly compatible with Python 3. Just add:

```
def __hash__(self):
    return id(self)
```

to Leaf and run 2to3. Only FieldTypeTestCase test fails. It may be worth mentioning in README.
