Fix problen with lost generators and rake tasks

Just setup gem as rails engine

Author: sedx

lib/haml-rails.rb

@@ -4,6 +4,8 @@
 
 module Haml
   module Rails
+    class Engine < ::Rails::Engine
+    end
     class Railtie < ::Rails::Railtie
       if ::Rails.version.to_s >= "3.1"
         config.app_generators.template_engine :haml