This change provides an option to add /dev/urandom to all architectures. The...

This change provides an option to add /dev/urandom to all architectures.  The pseudo-random algorithm I choose strikes an arguably-good balance between being "random" and small/fast enough for 8/16 bit MCUs.  It’s the well-documented xorshift128 algorithm.  It has an internal state of 128 bits that can be [re-]seeded with a write.