Merge pull request #20 from balanced/upgrade-gmp

bump gmp to 5.1.3, fixes #19
4c3d5dc76087416cee6793b7792633ab6c233b7e
Revert "4c3d5dc76087416cee6793b7792633ab6c233b7e"

This reverts commit 56c8eabec3ede013c7cb190de72cd9c021978e72.
upgrade the mpc and mpfr