Implement flake8-return

[charliermarsh]

• [ ] R501 ("do not explicitly return None in function if it is the only possible return value.")
• [ ] R502 ("do not implicitly return None in function able to return non-None value.")
• [ ] R503 ("missing explicit return at the end of function able to return non-None value.")
• [ ] R504 ("unnecessary variable assignment before return statement.")
• [ ] R505 ("unnecessary else after return statement.")
• [ ] R506 ("unnecessary else after raise statement.")
• [ ] R507 ("unnecessary else after continue statement.")
• [ ] R508 ("unnecessary else after break statement.")

See: https://pypi.org/project/flake8-return/

[charliermarsh]

Gonna bang this out real quick.