@rnd_geometric(p:int)
returns a random generator that produces integers following a geometric discrete distribution:

    P(i | p) = p (1 - p)^i,    i  ≥ 0.

See @rnd_bernoulli for a description of random generators.

See also Random Generators @rand,    @rand_int,    @random,    @rnd_bernoulli,    @rnd_binomial,    @rnd_exponential,    @rnd_gamma,    @rnd_geometric,    @rnd_normal,    @rnd_uniform_float,    @rnd_uniform_int