Multi-series histogram

[mcrascal]

Feature Description
What would you like to see added to Evidence?

Goal of Feature
Compare two distributions

Current Solution
Make two histograms

[mcrascal]

Initial thinking here is to add a "series" prop to the existing histogram component.

<Histogram data=... series='column' />

Some additional complexity in that the hist does it's own aggregations for counting and binning.