Add a new Section object to the config. Should be a subclass of
        _AbstractSection.

def add_section(self, section):
        """Add a new Section object to the config. Should be a subclass of
        _AbstractSection."""
        if not issubclass(section.__class__, _AbstractSection):
            raise TypeError("argument should be a subclass of Section")
        self.sections[section.get_key_name()] = section
        return section