Add predicates for reading and writing int8s and uint8s with binary file
streams.
Document the predicates that are used to write fixed size integer types
to text file streams properly.
library/io.m:
As above.
tests/hard_coded/Mmakefile:
tests/hard_coded/write_binary_uint8.{m,exp}:
tests/hard_coded/write_binary_int8.{m,exp}:
Test the new predicates.
