Add get_ident method to base throttle class

Fixed code example.

Let JSONEncoder handle Numpy data types.

For work on #1109.

Fixed #1105 -- Add hook for custom context in `BrowsableAPIRenderer`.

Replace hard coded response status check with `allow_form` context
variable, so that it can be overridden in a custom renderer class.

Typo in strings referring to Python package, django-filter.

On skip of django_filters related unit-tests the reason given states the Python package 'django-filters' is not install.

However, the Python package required to run django_filters related tests is 'django-filter'.

json.JSONEncoder cannot serialize Numpy data types. Numpy arrays
and array scalars have a tolist() method which casts the object to
a standard python data type.

Note on '.model' as default only, with 'serializer_class', and 'queryset' attributes prefered.  Closes #1100

Add order_by to the AutoFilterSet

small typo correction on ViewSet example code

`AutoFilterSet` should contains `order_by` set to all by default.