New 5.0 version. This merges the concept work done under

* Tests pass in Rails 3.0 to 3.2.
* Tests pass in Ruby 1.8 to 1.9.
* Follows intent from https://github.com/richmolj/acts_as_filterable/commits/master
* Interface change, switch from `filter_for_digits :attrib` to `acts_as_filterable :digits, :attrib`.
* Now uses a Railtie for load hooks. Only patch ActiveRecord when present.
* Added a dummy Rails application to test against.
* There is now only one `acts_as_filterable` class method added to ActiveRecord::Base! This also keeps non participating models from getting callbacks that they are not concerned with.
* Filters are applied to values coming right out of the database too!