add test case around ensuring proper field inference for boolean model field types
This fix results in models.NullBooleanField rendering as a checkbox in the browsable API
Fix expansion of writable nested serializers where the inner fields have source set.
Don't import compat.py from authtoken.models.  Closes #1297
Merge pull request #1298 from craigds/fix-nested-serializers-with-renamed-fields

Fix nested serializers with renamed fields
Typo
Add CONTRIBUTING.md
Merge branch 'master' of https://github.com/tomchristie/django-rest-framework
Merge pull request #1184 from dpetzel/nullbooleanfield_fix

Fix infered field type for models.NullBooleanField
Merge branch 'nullbooleanfield_testcase' of git://github.com/dpetzel/django-rest-framework into dpetzel-nullbooleanfield_testcase

Conflicts:
	rest_framework/tests/test_serializer.py
Use the BytesIO for buffering bytes and import the one from the compat module.
Merge pull request #1301 from linovia/bugfix/tutorial_for_python3

Fix tutorial's step 1 for Python 3
Add note on compat import in tutorial