Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_init_size.c

@@ -0,0 +1,28 @@
+#include "tommath_private.h"
+#ifdef MP_INIT_SIZE_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* init an mp_init for a given size */
+mp_err mp_init_size(mp_int *a, int size)
+{
+   size = MP_MAX(MP_MIN_DIGIT_COUNT, size);
+
+   if (size > MP_MAX_DIGIT_COUNT) {
+      return MP_OVF;
+   }
+
+   /* alloc mem */
+   a->dp = (mp_digit *) MP_CALLOC((size_t)size, sizeof(mp_digit));
+   if (a->dp == NULL) {
+      return MP_MEM;
+   }
+
+   /* set the members */
+   a->used  = 0;
+   a->alloc = size;
+   a->sign  = MP_ZPOS;
+
+   return MP_OKAY;
+}
+#endif