There are new flake8, pep8, twine, and transifex-client libraries in PyPI. DRF should use them.

In order to use them, the serializers module will have to no longer import * from relations and fields.

• Get rid of the import * syntax in serializers
• Update the PyPI packages
• Where we currently use serializers.Example, we will now use fields.Example or relations.Example if Example is a field or a relation that otherwise would have passed through the serializers module [We're not doing this]
• Create a .flake8 file with the equivalent of FLAKE8_ARGS = ['rest_framework', 'tests', '--ignore=E501'] and take it out of runtests.py

See #4613 for more information