this code needs a license

I would like to adopt the fsevents code with the intention of using it in [fsnotify](http://fsnotify.org/), which will hopefully [become part of the Go standard library](https://github.com/go-fsnotify/fsnotify/issues/1) in the future.

There was no LICENSE attached. How about Simplified BSD?

* [ ] Ian Wolfcat Atha @thatha
* [x] Nathan Youngman @nathany
* [ ] Peter Krnjevic @pkrnjevic
* [ ] Ron Burch @ronbu
* [ ] Sam Jacobson @samjacobson
* [ ] Steven Degutis @sdegutis

If this code does become part of the standard library, it would take on the same 3-clause BSD license as Go and all contributors would need to complete the [Google Individual Contributor License Agreement](https://cla.developers.google.com/about/google-individual).

P.S. If you would like to continue working on fsevents, that would be great.

This pull request should remain open until all existing contributors leave a comment in agreement.