Support direct putback of int8 and uint8 values to binary input streams
instead of via the bottom 8 bits of an int value.
library/io.m:
Add putback_{int8,uint8}/[34].
Add stream type class instances for putback streams binary_input_stream
with int8 and uint8.
tests/hard_coded/Mmakefile:
tests/hard_coded/putback_binary_int8.{m,exp}:
tests/hard_coded/putback_binary_uint8.{m,exp}:
Add tests of the above.
