Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_pack_count.c

@@ -0,0 +1,12 @@
+#include "tommath_private.h"
+#ifdef MP_PACK_COUNT_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+size_t mp_pack_count(const mp_int *a, size_t nails, size_t size)
+{
+   size_t bits = (size_t)mp_count_bits(a);
+   return ((bits / ((size * 8u) - nails)) + (((bits % ((size * 8u) - nails)) != 0u) ? 1u : 0u));
+}
+
+#endif