Add GBCli spec

GBCli is command line interface library for simplifying foundation tools. It provides classes for parsing and managing command line as well as possibility to use saved plists. Thus you can easily create layers of settings such as factory defaults, file settings, cmd line, all properly overriding each other.

Originally the code was implemented as part of my experimental appledoc (3.0) branch, but then I extracted it into separate library once I realized it could be useful for other folks too...