Intermediate stage where we know the old red black algorithm gives the
same results as the new algorithm and draws the grid at various
stages.
A hack implementation with an arrow from the initial grid to the
updated grid. Needs tidying as well as better (curved) arrows.
Merge Chris' change to hide exports only required for exposition.

Merge branch 'master' of https://github.com/idontgetoutmuch/Laplace

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