Update LibTomMath to 1.2.0 (#84) * update C files * update other files * update headers * update makefiles * remove mp_set/get_double() * use ltm 1.2.0 API * update ltm_desc * use bundled tommath if system-tommath is too old * XMALLOC etc. were changed to MP_MALLOC etc.

#include "tommath_private.h"
#ifdef BN_MP_ISEVEN_C
/* LibTomMath, multiple-precision integer library -- Tom St Denis */
/* SPDX-License-Identifier: Unlicense */

mp_bool mp_iseven(const mp_int *a)
{
   return MP_IS_EVEN(a) ? MP_YES : MP_NO;
}
#endif