Proper abstractions

[Tuomas Lukka <lukka@xxxxxxxxxx>]

Whew, finding the proper abstraction can make things a LOT easier.

One I just discovered is that going along a rank in two directions at
once (alternating), starting from a given cell is what made the vanishing
and row-column views so complicated. Abstracting this out to ZZIter made
such a difference (also of course separating rowcol from vanishing).

Now, we can start thinking about bootstrapping in an easier way since we
have that abstraction... I'm thinking of starting to code views first in
terms of cells to gain some experience.

	Tuomas