### SUMMARY

Update validate-modules to report messages using named error codes like `version-added` instead of error numbers like `E305`.

This would match the behavior of other tools we use, such as pylint, which have one named error code per rule. This will also make ignore entries much easier to read.

Doing this before 2.9 is released will avoid potential backwards compatibility issues with ignore entries in collections.

##### ISSUE TYPE

Feature Idea

##### COMPONENT NAME

validate-modules

if not self.base_branch or self._is_new_module():
            return
        with CaptureStd():
            try:
                existing_doc, dummy_examples, dummy_return, existing_metadata = get_docstring(self.base_module, fragment_loader, verbose=True)
                existing_options = existing_doc.get('options', {}) or {}
            except AssertionError:
                fragment = doc['extends_documentation_fragment']
                self.reporter.warning(
                    path=self.object_path,
                    code=392,
                    msg='Pre-existing DOCUMENTATION fragment missing: %s' % fragment
                )
                return
            except Exception as e:
                self.reporter.warning_trace(
                    path=self.object_path,
                    tracebk=e
                )
                self.reporter.warning(
                    path=self.object_path,
                    code=391,
                    msg=('Unknown pre-existing DOCUMENTATION error, see TRACE. Submodule refs may need updated')
                )
                return
        try:
            mod_version_added = StrictVersion()
            mod_version_added.parse(
                str(existing_doc.get('version_added', '0.0'))
            )