Add type hints

[jnewbigin]

This branch contains type hints to match click 8.1.7.

It also contains some other changes in order to get mypy running happily, including:

• adding mypy to the github actions workflow
• adding flake8 to the github actions workflow
• removing the parameters to calls to super()
• don't use a variable called help (shadows the global help command)
• update pyproject.toml to reflect the python versions being tested against
• update flake8 line length to match black (I have not run black on everything, but I have used black formatting on the function defs)

[edgarrmondragon]

Bump, this would be nice to have