Update docs/who_uses.rst

Added dbpatterns to who uses
Update configuration warning to mention defusedxml

This is mentioned in the README & docs but should also be mentioned in
the actual ImproperlyConfigured exception which is raised when you try
to use XML without all of the dependencies.
Added optional setting, 'TASTYPIE_ABSTRACT_APIKEY', which, if set to 'True', will make 'models.ApiKey' an abstract base class.
Included note re: syncdb when using ApiKey model. Closes #909.
Updates setup.py - corrects name of requirement

python-dateutil instead of python_dateutil
Fixes #884. Authorization for update should be only called once with a fully hydrated bundle
Fixes #850. Instead of using path to determin if we are dehydrating a list of resources or a single resource, we explicitly pass a boolean. This should also make writing tests easier as we no longer need to have path defined for requests.
Merge pull request #913 from ClearcodeHQ/master

Fixes requirement name
Only save related models if they've changed; closes #397, #594 and others.

Extra tests assuring through model metadata is saved; fixing backwards/forwards incompatability with MockRequest
Ignore the env3 virtualenv.
Backfilled release notes.
Added release notes for v0.9.15.
Bumped version to v0.9.15!
Started v0.9.16-dev.
Merge pull request #812 from fatiherikli/patch-1

Added dbpatterns to the Who Uses docs.