completed the spec

Hi Charles,

I've made a lot of changes to cover the GB spec more comprehensively, but used your basic Rule framework to do so.  The tests show the level of coverage.

I'll eventually need to make a few changes for slight modifications on the standard that SDGE has made.

Also packaged it as a gem (though haven't pushed it to a repo).

Let me know what you think, if you have questions,

Eric