(zone): Set `truncate-lines'.
Also, init `tab-width' with value from original buffer.
(zone-shift-up): Rewrite for speed.
(zone-shift-down, zone-shift-left, zone-shift-right): Likewise.
(zone-pgm-jitter): Remove redundant entries from ops vector.
(zone-exploding-remove): Reduce iteration count.
(zone-cpos): Convert to defsubst.
(zone-replace-char): New defsubst.
(zone-park/sit-for): Likewise.
(zone-fret): Take window-start arg.
Update callers. Use `zone-park/sit-for'.
(zone-fill-out-screen): Rewrite.
(zone-fall-through-ws): Likewise. Update callers.
(zone-pgm-drip): Use `zone-replace-char'.
Move var inits before while-loop. Use `zone-park/sit-for'.
(zone-pgm-random-life): Handle empty initial field.
Use `zone-replace-char' and `zone-park/sit-for'.