Add a --check flag to fail in CI if files need formatting

[elpete]

In a CI environment, we'd like to fail the build if there are any formatting changes CFFormat would make. We do not want to overwrite the formatting in CI because this would likely create git conflicts.

I see the message looking something like the following:

The following files do not match the cfformat rules:

/app/models/Foo.cfc
/app/handlers/Main.cfc

Please format the files using the `—overwrite` flag.