Support file exclusions via settings or .deprc

[mrjoelkemp]

This is the best bet for making the tool performant in large codebases. Sometimes, there are large vendor strewed about and we're constantly parsing those large things unnecessarily. Vendor files will never require your application code, but not all vendor files live in the default exclusions in node-dependents.

Pass the excluded paths to the node-dependents cli as a comma separated string