Change the compiler's big integer library to use libTomMath

This now replaces Bill's crappy big int implementation

src/libtommath/mp_clear.c

@@ -0,0 +1,20 @@
+#include "tommath_private.h"
+#ifdef MP_CLEAR_C
+/* LibTomMath, multiple-precision integer library -- Tom St Denis */
+/* SPDX-License-Identifier: Unlicense */
+
+/* clear one (frees)  */
+void mp_clear(mp_int *a)
+{
+   /* only do anything if a hasn't been freed previously */
+   if (a->dp != NULL) {
+      /* free ram */
+      MP_FREE_DIGS(a->dp, a->alloc);
+
+      /* reset members to make debugging easier */
+      a->dp    = NULL;
+      a->alloc = a->used = 0;
+      a->sign  = MP_ZPOS;
+   }
+}
+#endif