Jon's put the v4-5 Z-Machine Interpreter project on hold for a while.

The Z-Machine Interpreter is feature-complete for v3 games, though, so we have plenty to be testing and the z3 Inform Development Environment still works a treat too.

Here's the latest plan.

- Increase number of lines in MODE 0 from 31 to 32

- Split ROM into two versions:

1) BBC Micro Z-Machine Infocom v3-only Interpreter
Model B uses MODE 7 only, with remaining memory (after dynamic storage) used as cache
Model B+/Master 128 uses shadow MODE 0, with remaining memory (after dynamic storage) used as cache
If a v4 or v5 game is loaded, print an error message.

2) BBC Micro B+/Master 128 Z-Machine Infocom v3-5 Interpreter
MODE 0 with 2 selectable colours or MODE 1 with 4 selectable colours
Will use all 64K of sideways RAM for dynamic storage plus all main memory for cache.