Pass FSWatcher.path to notification callback

This pull request contains the change described in [https://github.com/3rd-Eden/fs.notify/issues/3](bigmonkeyboy's issue), which I'd argue is vital to the "not sucking hairy monkey balls" goal of the project, in that a callback, unable to tell on precisely which file it's receiving a notification, lacks enough utility that it can still be described as sucking at least one hairy monkey ball.

I acknowledge that there's no test included here, such as you requested from bigmonkeyboy. I'm not sure what you have in mind for such a test to cover, since your repo doesn't contain any preexisting tests on which to build. If you're unwilling to accept the pull request in its absence, then let me know what cases the test should include, and I'll submit another pull request with a test which meets those requirements.