Read settings from config file

The motivation is for this is to allow `coffeelint` config to be shared by `grunt/script coffeelint`, global `coffeelint` and inline linting via `AtomLinter`.

These commits are cherry-picked from the source repo. They allow `grunt-coffeelint` to be passed a config file in the same way regular `coffeelint` can. 

Another option might be merge all the new stuff from the source repo, but some of it conflicts with changes made in this fork.