Voronoi

[zmaril]

Add in voronoi detection to every svg element.
https://groups.google.com/forum/?fromgroups#!searchin/d3-js/tooltip/d3-js/-1oLMKUez3M/g3UjfyvKQIsJ
https://github.com/zmaril/d3-bootstrap-plugins/blob/master/src/js/plugins.coffee#L40

I've started working on it, should move it to another branch soon for development.