Set the angle of the sail to `angle` degrees

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

def set_sail(self, angle):
        '''
        Set the angle of the sail to `angle` degrees

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