Use standard format specifiers for 64bit ints

This fixes a bunch of stupid warnings.

It may also be worth considering the 16- and 32-bit versions for _w and
_s, but I didn't do them because it would've taken more than a 5-minute
search-and-replace to sort out which was which.

It may also be a good idea to come up with an urbit-standard name for
these rather than the ones given by inttypes.h. In that case, it's
easier to get there via search-and-replace if the standard ones are
already there.