@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