Since release candidate 3:
        - No changes, except minor documentary ones.

Since release candidate 2:
        - The .ipp files now use C-style comments, instead of Inform
coments, so that certain versions of cpp will not choke on them.  I do
not guarantee that Zig will build using any cpp (or any make, for that
matter).  But GNU versions should work.


Since release candidate 1:

        - Changed the stack size from 512 to 1024.  Now "Being Andrew
Plotkin" will not die from a stack overflow. [Thanks to Alex Warren
for the bug report.]

        - The verify code now computes the checksum on the pristine
game file. [Thanks to Joonas Pihlaja.]

        - The indirect variable references no longer pop or push the
stack.  They modify it in place.  [Thanks to Joonas Pihlaja.]

        - The sceen model has (unfortunately) undergone a large
change.  The windows are now buffered.  This allows us to implement
the sread opcode properly (if the game provides initial contents).
[Thanks to Andrew Plotkin's TerpEtude.]

        - I had the meaning of the "flag" operand to the tokenise
opcode reversed.  This resulted in some weird parser problems, which
are now fixed.

        - We now clear the screen when restarting.

        - z1 has been tested!  (I located a copy of Zork I, release 5.)