Use overridden settings exception handler

Instead of using the api_settings exception handler, we use the
overridden settings attribute to find the correct handler.

Closes #5054

fix whitespace in code example

Update Boolean field to support 'yes' and 'no' values

Python Reference:
distutils.util.strtobool(val)
Convert a string representation of truth to true (1) or false (0).
True values are y, yes, t, true, on and 1; false values are n, no, f, false, off and 0. Raises ValueError if val is anything else.

Fix parser names in docstring.

Fix typo at doc string

fix unique=True validation for ChoiceField

Add drfpasswordless to Third Party Packages and Authentication pages

Document adding django_filters to INSTALLED_APPS

Reminds users to add `django_filters` to their `INSTALLED_APPS` as detailed in the django-filter documentation https://django-filter.readthedocs.io/en/develop/guide/install.html

Fix docs 404 pages with nested paths.

JavaScript cleanup in API Docs.

use django 1.11rc1 in tox

Include URL path regexs in API schemas where valid.

Ensure that pagination is not included in API schema when `page_size=None`. 

Correctly set scheme in coreapi TokenAuthentication

Mention where the mixins live

Ctrl-F on the ViewSets page doesn't show where the `mixins.SomeMixin...` classes come from.