It was forgotten in #17 to apply this to siphash.c as well as halfsiphash.c. Note
that as-is this does change to a single 16-hex-char string for v0/1/2/3 in debug
output rather than having 8 then a space then 8. If preferred it can be changed
back to having the space and using `PRIx32` twice instead of `PRIx64` once.