[m-dev.] deprecating {read,write}_binary etc

[Julien Fischer]

Hi,

The predicates {read,write}_binary are currently implemented in a manner
which is (a) space efficient, (b) portable and (c) works with the non-C
backends.  (They currently work by calling io.write with a binary stream.)

I propose we mark them as obsolete.  While having a generic mechansim for
doing binary serialization of Mercury terms would be nice, what's 
currently there falls so short of the mark as to be useless.

Additionally, I propose that we also mark any predicates or functions that
manipulate bytes as the lower 8 bits of an int as obsolete; all such 
predicates or function should now have uint8 replacements.

Julien.