Variadic function for multiplications with mpz_t

[Hans Aberg]

> On 12 Jan 2015, at 23:36, Ha T. Lam <hatlam at gmail.com> wrote:
> 
> ​Unfortunately, there are a lot of GMP functions that are not available
> with ​the wrapper class, e.g. invert, gcd, nextprime, (non-negative) mod,
> etc. I end up converting between the C++ class and the C functions so often
> that I decided to go with the C functions instead, despite being not very
> comfortable with C.

With C++11 move constructor & assignment in the class, it is easy to add functions.