Flake8-return

* Port no-else-break, no-else-continue, no-else-raise, no-else-return from pylint (122) Calum Young
* PEP 621: Migrate more config to pyproject.toml (123) Christian Clauss
* Fix/116/R504-try-except (120) Calum Young
* Update ci (119) Calum Young
* Fix/47/Update-R504-for-assignment-value (117) Calum Young
* Upgrade GitHub Actions (113) Christian Clauss
* Add a space to avoid a typo in R503 (98) Christian Clauss
* GitHub Action to lint Python code (97) Christian Clauss
* Typo fixes (92) Aarni Koskela
* Create codeql-analysis.yml Afonasev Evgeniy
* Bump flake8-plugin-utils from 1.1.1 to 1.3.2 (87) dependabot
* Bump mypy from 0.812 to 0.971 (114) dependabot
* Bump pytest-cov from 3.0.0 to 4.0.0 (124) dependabot
* Bump pytest-cov from 2.11.1 to 3.0.0 (102) dependabot
* Bump pytest-mock from 3.6.0 to 3.6.1 (91) dependabot
* Bump pytest from 6.2.4 to 6.2.5 (99) dependabot
* Bump pylint from 2.8.2 to 2.10.2 (100) dependabot
* Bump pytest from 6.2.3 to 6.2.4 (86) dependabot

* Error clarifications (77) Clément Robert
* fix linting (migrate to black 20.0b1) (78) Clément Robert

Make R504 visitors handle while loops (56) kageurufu
Rename allows-prereleases to allow-prereleases (55) kageurufu

* skip functions that consist only `return None`
* fix false positive when last return inner with statement
* add unnecessary assign error
* add support tuple in assign or return expressions
* add suppport asyncio coroutines