Should "select by tag" return list of 2D arrays, 1 3D array, or a summed 2D array?

[e-lo]

I think we probably would like capabilities on all fronts, but for trips (and other additive measures) we most likely want a summed 2D array while for something like a skim, we would probably like to be able to iterate through the list (simpler than a 3D array, although not all numpy functionality comes through).

[bstabler]

I'm closing this since we should move this issue to https://github.com/osPlanning/omx-python