Turns out there's a bit of code that isn't compatible w/ the Python version,
eliminate it...  This was to support encoding lengths (via negative length
parameters)...

Also, the default C version (which we want to use) is Keccak(800) and not
Keccak(1600), switch Python to 800, as it'll be faster on the 32-bit uC, and
still has plenty of security margin...