Add error codes to `APIException`

Corrected `artist` and `album_name` typo in docs

`The Roots` are the band: https://en.wikipedia.org/wiki/The_Roots

`Undun` is their album: https://en.wikipedia.org/wiki/Undun

* Start test case

* Added 'requests' test client

* Address typos

* Graceful fallback if requests is not installed.

* Add cookie support

* Tests for auth and CSRF

* Py3 compat

* py3 compat

* py3 compat

* Add get_requests_client

* Added SchemaGenerator.should_include_link

* add settings for html cutoff on related fields

* Router doesn't work if prefix is blank, though project urls.py handles prefix

* Fix Django 1.10 to-many deprecation

* Add django.core.urlresolvers compatibility

* Update django-filter & django-guardian

* Check for empty router prefix; adjust URL accordingly

It's easiest to fix this issue after we have made the regex.  To try
to fix it before would require doing something different for List vs
Detail, which means we'd have to know which type of url we're
constructing before acting accordingly.

* Fix misc django deprecations

* Use TOC extension instead of header

* Fix deprecations for py3k

* Add py3k compatibility to is_simple_callable

* Add is_simple_callable tests

* Drop python 3.2 support (EOL, Dropped by Django)

* schema_renderers= should *set* the renderers, not append to them.

* API client (#4424)

* Fix release notes

* Add note about 'User account is disabled.' vs 'Unable to log in'

* Clean up schema generation (#4527)

* Handle multiple methods on custom action (#4529)

* RequestsClient, CoreAPIClient

* exclude_from_schema

* Added 'get_schema_view()' shortcut

* Added schema descriptions

* Better descriptions for schemas

* Add type annotation to schema generation

* Coerce schema 'pk' in path to actual field name

* Deprecations move into assertion errors

* Use get_schema_view in tests

* Updte CoreJSON media type

* Handle schema structure correctly when path prefixs exist. Closes #4401

* Add PendingDeprecation to Router schema generation.

* Added SCHEMA_COERCE_PATH_PK and SCHEMA_COERCE_METHOD_NAMES

* Renamed and documented 'get_schema_fields' interface.

* Fix rest_framework.filters.OrderingFilter doesn't pass context to serializers #4541

* #4541 Additional fix for remove_invalid_fields()

Update Django security release 1.10.2

- enabling validtions on incoming query params with the ease of adding new filters as easy as adding a new key in a dict.

Update Django security releases 1.9.10 and 1.8.15

Rename an invalid reference to BasicToken in the docs

This commit allows `response.render` to be called when
`response.rendered_context == {}`. This should be allowed, since
if [the JSONRenderer, for example](https://github.com/tomchristie/django-rest-framework/blob/master/rest_framework/renderers.py#L85-L92) receives a `None` context, it
sets it to an empty dictionary itself.

In commit 5392be4d, there was a change
made when cleaning up the template for the API listing that caused 2
spaces to appear before every header item (except the first) and before
the first line of the body of the response. This meant that it often
looked like:

HTTP 200 OK
  Allow: GET, OPTIONS
  Content-Type: application/json
  Vary: Accept

  {
    "key": "value",
    "key2": "value2"
}

This change removes those leading spaces, so that it will now look like:

HTTP 200 OK
Allow: GET, OPTIONS
Content-Type: application/json
Vary: Accept

{
    "key": "value",
    "key2": "value2"
}

* Don't deepcopy 'regex' arguments, instead treat as immutable.