Add subok and other np.array parameters
subok also for __quantity_view__, __quantity_instance__; more tests
Propagation of __quantity_view__, instance__ to subclasses
Simplify Quantity subclassing API, replacing __quantity_view__ and
__quantity_instance__ with __quantity_subclass__ and __quantity_finalize__.
Simplify _new_view, _new_instance further, remove __quantity_finalize__
Further simplification, using only _new_view
Simplify __quantity_subclass__ a little
Add tests for quantity.view; use _unit in __array_finalize__
Pass unit through Unit (fast if UnitBase already); use to simplify further
Add a brief summary about how to subclass quantity to the documentaion
Update subclass documentation following comments from @eteq
Further update to quantity subclassing documentation
Merge pull request #2270 from mhvk/quantity-subok

Quantity subok, and replace __quantity_view__, __quantity_instance__