Extracted from Pensive project

This library was originally written as part of a Sprite Kit game
(message passing between sprites, etc). Since it has become so useful,
I decided to export it to its own library and then re-import it as a
submodule in further projects.
Updated license

Added 2013 year (was just 2014)
Updated readme

Added a quick rundown of the relevant interface and protocol items, in
case anyone else wants to play with this.