accordingly.

- Add pre-commit check for out-of-date dependencies.
- Add flake8 pre-commit check.
- List roles needed for testing (bootstraping) at
tests/requirements.yml, leave other dependencies at meta/main.yml.
- Update molecule.yml, ansible.cfg for newer versions of Molecule.
- Update documentation, playbook accordingly.

  issues:
  - Missed a blank line between tests in `tests/test_example.py`.
  - Named the assertions task.
- Updated the OpenBSD Vagrant box to 6.0, updated assertion accordingly.

- Enabled diff.