Fix DocBlock for derived classes

[ostrolucky]

This goes hand in hand with #91

If you add new method in your derived class, IDE without this patch doesn't know it's there after you call some fluent method.

[Ocramius]

This is an interface change, as it prevents child classes from returning an instance of the parent class.

Closing as invalid.

Also note that static is not a type hint, while self and parent are.