Adds ::rollback method to Songkick::Oauth2::Schema

Also updates README to indicate the availability
of the rollback method.

(Also aliased as ::down)

Author: gregates

README.rdoc

@@ -113,6 +113,8 @@ the gem's migrations that have not yet been applied to your database.
      -> 0.0009s
   ...
 
+To rollback migrations, use <tt>Songkick::OAuth2::Model::Schema.rollback</tt>.
+
 
 === Model Mixins
 

lib/songkick/oauth2/schema.rb

@@ -10,6 +10,14 @@ class << self
         alias :up :migrate
       end
 
+      def self.rollback
+        ActiveRecord::Base.logger ||= Logger.new(StringIO.new)
+        ActiveRecord::Migrator.down(migrations_path)
+      end
+      class << self
+        alias :down :rollback
+      end
+
       def self.migrations_path
         File.expand_path('../schema', __FILE__)
       end