Set a user's avatar.

        :param username: the user to set the avatar for
        :param avatar: ID of the avatar to set

def set_user_avatar(self, username, avatar):
        """Set a user's avatar.

        :param username: the user to set the avatar for
        :param avatar: ID of the avatar to set
        """
        self._set_avatar(
            {'username': username}, self._get_url('user/avatar'), avatar)