Loading the grid subsystem on top of the TRS-80 driver, which is
an interface to its ROM BIOS, would be counter-productive because
the BIOS already has the concept of cursor.

However, VE needs the Grid interface, so we implement a shim for it.

Again, all this work (and the re-assembly that it entails) has been
done from within Collapse OS on the TRS-80!

Working in "blk/" folder from a modern system is harder than it
should be. Moving blocks around is a bit awkward, grepping is a
bit less convenient than it could be, git blame has troubles
following, etc.

In this commit, we modify blkpack and blkunpack to work with single
text files with blocks being separated by a special markup.

I think this will make the code significantly more convenient to
work into.