clean databases to ensure a clean state for testing

 Strategies for cleaning databases. Can be used to ensure a clean state
 for testing.
 .
 Each strategy is a small amount of code but is code that is usually needed
 in any ruby app that is testing with a database.
 .
 ActiveRecord, DataMapper, Sequel, MongoMapper, Mongoid, CouchPotato, Ohm and
 Redis are supported.