List enrolled courses.

        @return: List of enrolled courses.
        @rtype: [str]

def list_courses(self):
        """
        List enrolled courses.

        @return: List of enrolled courses.
        @rtype: [str]
        """
        reply = get_page(self._session, OPENCOURSE_MEMBERSHIPS, json=True)
        course_list = reply['linked']['courses.v1']
        slugs = [element['slug'] for element in course_list]
        return slugs