Fix the bug where cd's were getting written in twice instead of being overwritten when the title or artist name was edited.
Add Genre class.
Add small cosmetic changes to the cd specs and readme.
Add initialize and read/write name methods for Genre class.
Add a couple more cosmetic changes to cd spec.
Create add_cd method to add a cd object to the genre's library of cds, and a library method to return an array of the added cds.
Add behavior to the genre's add_cd method so that cd objects are not added more than once.
Add .all class method to Genre to return all Genre instances.
WIP: Add ui options related to genre.
Add delete cd and delete genre methods to Genre class.