Add check argument

[jamescurtin]

By specifying the --check argument, the program will exit with a code of 1. This is useful if using as part of a CI pipeline that should fail if changes are necessary.

[coveralls]

Coverage decreased (-0.2%) to 99.324% when pulling a1c08a2 on jamescurtin:add-check-argument into 5130533 on myint:master.

[myint]

It seems like this would be equivalent to running pyflakes directly.

[jamescurtin]

I think there are a few differences. It is possible that autoflake will only try to fix a subset of issues that pyflake discovers, due to usage of CLI options and # noqa hints. I am not aware of an easy approach to coerce pyflake to only warn about issues that autoflake is configured to correct.

The use case I'm considering requires that contributors to a project run a suite of tests & linting tasks before being allowed to merge a PR. Using pyflake here could potentially prevent someone from merging due to a false positive.

Thoughts on this? And thanks for reviewing!

[myint]

Makes sense to me. Thanks!