Adjusted notifyUser function for readability and JSdoc

I spent a while to find the correct form, this is the form suggested by
Google Closure
https://developers.google.com/closure/compiler/docs/js-for-compiler?csw=
1
http://stackoverflow.com/questions/4729516/correct-way-to-document-open-
ended-argument-functions-in-jsdoc

And used by lodash
https://github.com/lodash/lodash/blob/master/lodash.js#L5581