Set the angle of the rudder to be `angle` degrees.

        :param angle: rudder angle
        :type angle: float between -90 and 90

def set_rudder(self, angle):
        '''
        Set the angle of the rudder to be `angle` degrees.

        :param angle: rudder angle
        :type angle: float between -90 and 90
        '''
        angle = float(angle)
        request = self.boatd.post({'value': float(angle)}, '/rudder')
        return request.get('result')