An example of how to link multiple beeswarm plots, which could be used to instead of parallel plots if the distribution across each category is important. This implementation hides the connections until a unique series is chosen, but it could be set show the connections (with some opacity) if there are trends worth showing. Uses voronoi follow click events. Based on /mbostock/6526445e2b44303eebf21da3b6627320
forked from tomshanley's block: Mutliple connected beeswarm plots