pwiz fails to generate correct code: UnknownField
```
createdb
psql <<EOF
CREATE TABLE example (
  address inet DEFAULT '0.0.0.0'::inet NOT NULL PRIMARY KEY
);
EOF
python -m pwiz -e postgresql -u $USER $USER
```

generates the following code:

```
class UnknownField(object):
    pass

class BaseModel(Model):
    class Meta:
        database = database

class Example(BaseModel):
    address = UnknownField(primary_key=True)  # inet
    class Meta:
        db_table = 'example'
```

UnknownField blows up because it expects named args and it has no initializer.
it should be:

```
class UnknownField(object):
    def __init__(self, **kwargs):
        pass
```
