Add [linter]_args option

[samuelmeuli]

This option could allow users to pass additional command-line arguments to the linting command. E.g. useful if users want GitHub checks to fail if there are warnings (see #10).

[nocalla]

Would this also allow configuration of linters? E.g. adding a line-length argument to black?

[samuelmeuli]

Yes, but I think it's better to use a configuration file instead. That way, your options are applied both in CI and when runnung Black locally.

[nocalla]

Good point.