Second re-write

There will be a third.

This baselevel brings up TOPS-10 and TOPS-20 and they seem to run fairly
reliably, though not yet load-tested.

Code has been refactored - needs another pass.  Start at documentation.

Still needs to move processing into the service loop.

NB. You need to add set kmc0 ena AFTER set kmc ena for it to come
on-line.
Try show kmc as well.