fun-size crypto nybles and bytes..for small systems

#1switch over to bignum library from single precision arithmetic

Forth arbitrary precision arithmetic library:

Contenders: * https://github.com/Lehs/BIG-INTEGER-ANS-FORTH * https://www.taygeta.com/fsl/sciforth.html * mecrisp-stellaris bignum

Lehs' library looks like it has the WORDs needed for the job.