Update version number to 0.003.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Use FastCalc as a fallback to GMP.

RT #82714 pointed out that the pure-Perl implementation is very slow.  FastCalc
is also very slow, but presumably faster than Calc.  GMP is definitely the
preferred Math::BigInt implementation still.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>