Filter for space-filling-curves

[mrocklin]

ND-arrays representing spatial data may have highly related data located spatially in an n-dimensional sense. It's possible that pre-ordering the buffer with some sort of space-filling curve would improve compression.

[alimanfoo]

I think there is overlap with #40 where @shoyer proposed re-ordering each chunk's buffer using the Z-order curve, except here the goal is to improve compression and in #40 the goal is to reduce overhead associated with accessing small data regions.

Looks like there was some discussion of adding support for Z-ordering (Morton ordering) to numpy a while back, but looks like it didn't go anywhere. There is some code by @tgamblin.

cc @benjeffery