* Setting Ruby version and gemset for rvm
* Renamed original migration
* Added another migration for upgrades that adds a comments field
* Updated the instance methods injected into an acts_as_nps_rateable model so they can handle arbitrary subsets of ratings when calculating promoters, detractors, passives and the nps rating
* Moved from copying over an NpsRating class into the rails project to using a gem-embedded ActsAsNpsRateable::NpsRating class instead.  Extend it for custom behavior by adding a Decorator.
* Added the .calculate_for method which determines the nps rating for a given set of NpsRatings
* Bumped the version to 0.0.2