Feature Request: allow building hanat tree using quantitative data (mean instead of sum)

[gdevenyi]

The entire hanat implementation appears to be currently centered around "Volumes".

We are now working with various quantitative metrics and it would be nice to represent them in the same tree, but the tree construction appears to be "sum only" right now.

[bcdarwin]

related: #308

[jasonlerch]

Agreed completely. I have code that I'll commit within a week or so for testing.