pochhammer: Calculate the value of Pochhammer's symbol
Description
pochhammer returns the value of Pochhammer's symbol calculated as
$$\left( z \right)_n = z\;\left( {z + 1} \right)\; \ldots \;\left( {z + n - 1} \right) = \frac{{\Gamma \left( {z + n} \right)}}{{\Gamma \left( z \right)}}$$
where $\Gamma \left( z \right)$ is the Gamma function