Simplify the implementation of parallel merge-sort, so that we have one pass per
swap across chunks. Use a data join so that the elements are translated rather
than rotated, since this better conveys the underlying sort. Auto-play the
animation in parallel, and restart a few seconds after it finishes.
Inspired by the phrase "reminiscent of wind gusting over tall grasses" in
<http://vis.stanford.edu/protovis/ex/sort.html>.
It seemed abominable not to animate the swaying tall grasses!