zuse: schnorrsig-sign from spec
zuse: schnorrsig-sign from spec

test vectors match, but are byte-flipped. has to do a lot of endianness
twiddling.

ngzax/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit,urbit/urbit,urbit/urbit,urbit/urbit,ngzax/urbit,urbit/urbit,ngzax/urbit,ngzax/urbit,urbit/urbit