If the remainder of the division of the current BarNumber by the
first argument of modulo-bar-number-visible equals its second
argument print the BarNumber.
Useful to print the BarNumber at certain distances, p.e.:
(modulo-bar-number-visible 3 2) -> prints 2,5,8(modulo-bar-number-visible 4 2) -> prints 2,6,10(modulo-bar-number-visible 3 1) -> prints 3,5,7(modulo-bar-number-visible 5 2) -> prints 2,7,12