Add missing csrf_token in AdminRenderer post form.

Markdown compat (overtakes #3604)

Conflicts:
	requirements/requirements-optionals.txt

Fix update model example in html-and-forms.md

Added explicit id field in multi update example

Update license year range to 2016

Update permissions.md

Adding additional note about the behavior of set permission classes per view as suggest on #3834

QueryParameterVersioning does not use default version

QueryParameterVersioning does not fall back to the value used in the `DEFAULT_VERSION` setting, while other versioning schemes do. This looks like a minor change, and incorporates the `self.default_version` set in the superclass.

I'll sheepishly admit that I edited this inline without running any tests or anything, so please let me know if this needs more work.

Display py.test internal warnings

Regarding #3729

Document how to tweak authtoken.admin.TokenAdmin

python -Werror generates warnings informing that on_delete is a required keyword in Django 2.0

With focus on large user base, but can be extended.

2015 update in __init__.py file

update copyright 2016

Fixed TimeField not handling empty values

PY2: DateField.to_representation can't work with unicode value

Fixes #3786

Added documentation for the third party jsonapi.org package

Fix nested validation error being rendered incorrectly.

Minor fix for dictionary key lookup in settings file

Fixes #3804, avoiding update of Meta.extra_kwargs

Added unit test to cover.

Typo fix in docs/api-guide/relations.md

`slug field` in code snippet was replaced to `slug_field`

Previously an extra list wrapped nested validation errors raised from serializer's validate() methods.
That was inconsistent with the format of validation errors raised by validate_<fieldname> methods.
i.e. these two resulted in *different* behaviour:

    def validate_foo(self):
        raise ValidationError(['bar'])

    def validate(self):
        raise ValidationError({'foo': ['bar']})

don't import authtoken model until needed