add flake8 and setup.cfg for linting

some changes to pass flake8 linting. added setup.cfg for flake8
configuration. Ignoring E265 can be added to this file because
config/settings.py is flooded with this error. After #105 gets
merged it'll be OK.
added myself to CONTRIBUTORS.txt
Merge pull request #122 from slafs/linting

add flake8 and setup.cfg for linting