Add Style enforcer (via Rubocop)

It will fail the build, but as it is currently,
most of the cops are 'todos'. Great for new contributors.. :)

lib/generators/serializer/templates/serializer.rb.erb

@@ -0,0 +1,8 @@
+<% module_namespacing do -%>
+class <%= class_name %>Serializer < <%= parent_class_name %>
+  attributes <%= attributes_names.map(&:inspect).join(", ") %>
+<% association_names.each do |attribute| -%>
+  has_one :<%= attribute %>
+<% end -%>
+end
+<% end -%>