divergence matrix

[jeromekelleher]

The StatsCalculator interface defined a divergence_matrix function. Add this back in and test.

It is possible to get all pairs easily enough using itertools.combinations(), but this seems like a useful thing to have.

[jeromekelleher]

From @petrelharp in the comments of #194:

Do we even need divergence_matrix? It would be nice to have some way to make it easy for people to get all combinations, but maybe that could be another argument? Like, indices = "all"?

[jeromekelleher]

Pushing this out to 0.2.1.

[jeromekelleher]

Pushing this out again. @petrelharp, do we really want this? Seems easy enough to replicate, and maybe a good tutorial example rather than needing a native method?

[petrelharp]

Sounds good to me - put it in a tutorial.