Visual Editor

This editor, unlike the Block Editor (B100), is grid-based
instead of being command-based. It requires the AT-XY, COLS
and LINES words to be implemented.

It is loaded with "125 LOAD" and invoked with "VE".

This editor uses 17 lines. The top line is the status line and
the 16 others are contents lines. The content shown is that
of the currently selected block.

All keystrokes are directly interpreted by VE and have the
effect described below.

                                                        (cont.)