Computes the non-negative angular distance between x and y. With the
default period, values are returned in [0, pi].
See also
Other angle utilities:
angular_difference(),
check_angle(),
compass_to_rad(),
deg_to_rad(),
hour_to_rad(),
is_angle(),
normalize_angle(),
rad_to_compass(),
rad_to_deg(),
rad_to_hour()