It bothers me a little bit that I can't figure out how to free the
parser --- surely that is a thing that the bindings for other
languages need to do --- but storing a pointer to the parser in a
statically-allocated variable, as in base64.c, at least stops valgrind
from reporting the parser as a memory leak.

I don't think these actually affect correctness since there's no way for
0x40 or 0x60 to show up in a parse tree anyway, but they're confusing.

effects throughout, including use of inttypes.h/PRI[ud]64 because printf() is
still stuck in a long world, conversion of %lu to %zu for printing values of
type size_t, and changing/renaming the g_check_cmp* family of functions.