allow explicitly ignoring directories

[jhackshaw]

Add option to explicitly ignore folders from being checked.

My use case is for the netlify-cms plugin with a gatsby project. It automatically includes a bunch of files under /admin that I don't want to check, but I do want to check every other page on the site.

With these changes, I would configure the plugin like this:

[plugins.inputs]
checkPaths = ['/']
ignoreDirectories = ['/admin']

[swyxio]

lgtm! will ship in next minor