Add a Module#module_function spec
Fix Module#module_function on Class
Simplify a Module#included spec
Add a Module#append_features spec
Add a Module#extend_object spec
Fix Module#{append_features,extend_object} on Class
Add Module#prepend_features specs

related ruby/ruby#376
Fix Module#prepend_features
Add a Module#prepend spec
Fix Module#prepend visibility
Write a Module#prepended spec
Fix Module#prepended visibility