adding :through option to replace :nesting option and moving ResourceAuthorization class code into ControllerResource

allow access to classes when using hash conditions since you'll generally want to narrow it down with a database query

removing unauthorized! in favor of authorize! and including more information in AccessDenied exception - closes #40

renaming ActiveRecordAdditions#can method to accessible_by since it flows better and makes more sense

adding caching to current_ability class method, if you're overriding this be sure to add caching there too

adding can method to Active Record for fetching records matching a specific ability, still needs documentation

renaming :class option to :resource for load_and_authorize_resource which now supports a symbol for non models - closes #45

allow additional arguments for be_able_to matcher, this requires Ruby 1.8.7 or higher to use matcher

Adding :class option to load_resource so one can customize which class to use for the model - closes #17

Don't fetch parent of nested resource if *_id parameter is missing so it works with shallow nested routes - closes #14

Adding :collection and :new options to load_resource method so we can specify behavior of additional actions if needed.