Support "path" arg

[scottrippey]

From the CLI, it would be great to be able to do something like:

remove-git-ignored [PATH]

This would allow me to easily remove "sections" of ignored code; eg:
package.json

...
  "scripts": {
    "test:clean": "remove-git-ignored test",
    "build:clean": "remove-git-ignored build",
  }

I know I can do this, currently, with cd test && remove-git-ignored, but it would be more intuitive if the syntax was more similar to rm -r.