This function returns a random variate from the Landau
distribution. The probability distribution for Landau random
variates is defined analytically by the complex integral,
\[p(x) = (1/(2 \pi i))
\int_{c-i\infty}^{c+i\infty} \exp(s \log(s) + x s) ds\]
For numerical purposes it is more convenient to use the following
equivalent form of the integral,
\[p(x) = (1/\pi) \int_0^\infty \exp(-t \log(t) - x t) \sin(\pi t) dt.\]