* Refactor logic for attaching a `Method` class as a property rather than a method. Instead of implicitly setting `mungers=None`, explicitly set the `is_property` flag on `Method` to `True`. This also facilitates attaching new methods and properties to modules.

* Fix up some tests in test_method.py that were falsely passing to actually test correctly. Add tests for new `is_property` flag for the `Method` class.

* Create `test_module.py` and add tests for `attach_methods()`