Dirty-models

- Added a easy way to get model structure. It will be used by autodoc libraries as sphinx or json-schema.

- Added autolist parameter to ArrayField. It allows to assign a single item to a list field,
so it will be converted to a list with this value.

python

class ExampleModel(BaseModel):
array_field = ArrayField(field_type=StringField(), autolist=True)

model = ExampleModel()
model.array_field = 'foo'
assert model.array_field[0] is 'foo'