Removed a mutable default param in Serializer.serialize().

I haven't seen this pop up explicitly as a bug in code; only noticed it
through code inspection.
Raise ApiFieldError on invalid datetimes
If no object_class is present, do not try to instantiate an object when building the bundle. This does not affect model-based resources; however, the assumption that had been made that an object_class is always going to be present is not valid when using custom Resource objects that are not necessarily model-based.
Adding OAuth 2.0 tutorial information in cookbook
Unprocessable entity http code
added None value for username_field when ImproperlyConfigured
error occurs so it wont give an ImportError
add detail_uri_name to Non-PK URL example

This is a crucial detail missing that ought to be included in the example. The resource_uri generated from the example and included in the response is inherently incorrect, given the desired result. EG, if you want to use a non-pk you want to query a ModelResource like this, you'll want the resource_uri updated. If you don't, hopefully you'll notice that the example includes meta.detail_uri_name :)
fixes #959, Authorization calls create_detail twice
Added test case to demonstrate resources without object_class defined failing on build_bundle
Made proper test for checking Resource objects without a defined object_class.
Merge pull request #960 from svleeuwen/master

Fix for issue #959, create_detail should only be called once by authorization
Merge pull request #956 from illumin-us-r3v0lution/patch-1

added detail_uri_name to Non-PK URL example
Merge pull request #946 from w43l/master

error importing username_field
Merge pull request #928 from RentMethod/httpUnprocessableEntity

HTTP 422 Unprocessable Entity
Merge branch 'master' of git://github.com/ianalexander/django-tastypie into ianalexander-master
Fixing title underline.
Merge pull request #877 from terpsquared/master

Fixed assumption that breaks non-model based resources during bundle building
Fixes #926, #976, #926 and others.
defusedxml is now a requirement if you wish to support xml requests.
Merge pull request #994 from georgedorn/defusedxml_docs

Fixes #926, #976, #926 and others.
Bumped to v0.9.16!