Provides support for big integer calculations by means of the GMP library, as
a replacement (drop-in) module for Math::BigInt's core, Math::BigInt::Calc.pm.
Math::BigInt::GMP does not use Math::GMP, but provides its own XS layer to
access the GMP library. This cuts out another (perl subroutine) layer and
also reduces the memory footprint by not loading Math::GMP and Carp at all.