nml: convert arch-dependent types to fixed-width types

.. when they are related to types that pass over the wire in nml.

include stdint.h as needed.

use inttypes.h integer formatting string constants as appropriate.

Signed-off-by: Jeff Epler <jepler@unpythonic.net>
tests: this test now passes on 64-bit platforms

Signed-off-by: Jeff Epler <jepler@unpythonic.net>