Auto-generated primary key not returned by the Model

[seapagan]

If create_pk is True, an autogenerated PK (defaults to id) is created. However this is not exposed on the return model from a query, so methods like update() or delete() that require a primary key cant be called in this case (if the Model has a custom named PK then that works).

After a lot of thought, this will be fixed by making the auto-generated pk compulsory and removing the option to rename it. The ability to rename or remove the auto-increment field may be added again in future releases once the code is cleaned up a bit.

Work on this is in #39 which will close this when complete

[seapagan]

fixed by #39. This makes the 'pk' field NON OPTIONAL