feat: Support setup.py files (#2805)

.gitignore

.travis.yml

lib/config/definitions.js

lib/manager/index.js

lib/manager/pip_requirements/extract.js

lib/manager/pip_setup/extract.js

lib/manager/pip_setup/extract.py

lib/manager/pip_setup/index.js

lib/util/ignore.js

requirements.txt

test/_fixtures/pip_setup/setup.py

test/manager/pip_setup/__snapshots__/extract.spec.js.snap

test/manager/pip_setup/extract.spec.js

...rkers/repository/extract/__snapshots__/index.spec.js.snap

website/docs/configuration-options.md