fix function names and dotted lookups for use in PrimaryKeyRelatedField.field_to_native (they work in RelatedField.field_to_native already)
Allow for missing non-required nested objects.

Serializer fields which are themselves serializers should not be required.
Specifically, if a nested object is set to "required=False", it should be
possible to serialize the main object and have the sub-object set to None/null.
Test and fix which closes #652.
Version 2.3.3
Merge branch 'master' of https://github.com/tomchristie/django-rest-framework
HyperlinkedIdentityField uses `lookup_field` kwarg.

According to the [Serializers API Guide][1], `HyperlinkedIdentityField`
takes `lookup_field` as a kwarg like the other related fields and the
generic views. However, this was not actually implemented.

[1]: http://django-rest-framework.org/api-guide/serializers.html#hyperlinkedmodelserializer
Merge pull request #844 from rouge8/hyperlinkedidentityfield-lookup_field

HyperlinkedIdentityField uses `lookup_field` kwarg.
Added @rouge8 for bugfix #844.  Thank you!
Update release-notes.md
Updated README.md
Fix typo + grammar in viewsets docs
Merge pull request #847 from johtso/patch-1

Fix typo + grammar in viewsets docs
PendingDeprecation warning to allow_empty
Fix PendingDeprecation warnings in tests
Minor mixin refactoring
Merge remote-tracking branch 'upstream/master'
Forms in Broseable API support dynamic serializers based on request method
Merge pull request #850 from tomchristie/dynamic-forms

Forms in Broseable API support dynamic serializers based on request method
Updated the dependencies version and added the ALLOWED_HOSTS for tests.
add tests for related field source for RelatedField and PrimaryKeyRelatedField. #694