Reorganised object code loader/linker to make it much more modular and
cleaner.  All the machinery is now in object.[ch].  This stuff is
packaged up as close to a standalone library as I can reasonably get
it -- in particular, it knows nothing about Hugs -- so that the linker
could easily be used in some entirely different application with
almost no changes, if we so desire.

Minor mods to interface.c & storage.c to use the new linker API.