Add a Severity to the project and returns a :class:`Severity` object.

        :param name: name of the :class:`Severity`
        :param attrs: optional attributes for :class:`Severity`

def add_severity(self, name, **attrs):
        """
        Add a Severity to the project and returns a :class:`Severity` object.

        :param name: name of the :class:`Severity`
        :param attrs: optional attributes for :class:`Severity`
        """
        return Severities(self.requester).create(self.id, name, **attrs)