Inheritance is supported, albeit in a somewhat limited way. Methods
(instance and static) are inherited as you would expect. Fields in a
super class will be inherited into the subclass, where you can augment
the fields tuple or change the database type (by specifying the field,
but with a different database type). This second form may or may not
be supported in future releases. The unique is inherited, but setting
it will override, not augment, the super class' definition.
Inheriting from multiple PyDO classes is undefined as to the real
behavior. It may work, but no guarantees.
