Debug mode:

o would like to be able to single-step a step-list, with display
  after every step.

o should turn every "run" into a breakpoint, with display before and
  after each run: each "run" becomes

        save-site-src site-src site run kick restore-site-src show
        run show

o should also turn every "breakpoint" into a breakpoint

o could do this by modifying a step-list so that each run is an end,
  and the head pointer keeps changing.



notation:

debug-step on

define-step eg-step
        .
        .
        .
        breakpoint      \ ignored if not in debug-step
        .
        .
        .
        run
        .
        .
        .
end-step

debug-step off


o add a control-panel key to show which subcells are active, what the
  current kick is for each subcell bit, what the source is for each bit,
  and what the source is for each bit of the lut and the event counter.