Allow user to sort balances by variance explained

[tpq]

Currently, balances get sorted by proximity to base. I could add an argument that allows the user to sort balances by the amount of variance explained.

[tpq]

Reviewer writes,

However, it seems useful to have a tool allowing alphanumerical output of ordered variances or cuts of the partition tree.

Perhaps a top argument that subsets the top N balances directly?