When circularizing a way, try to add inBetweenNodes to shared ways too..
Add 2D cross product to iD.geo..
Add isConvex() to iD.Way..
Add d3.geom.hull to d3.v3.js
Coax concave ways to convex before circularizing..
Factor makeConvex into new method, fix missing comma and style issues..
Add tests for iD.geo.cross and iD.way.isConvex
Require 2 uniq points for circularize.  Handle 2 point case, where D3 centroid() fails.
Fix isConvex() to correctly test the angle that closes the way.
Add tests for circularizing concave ways, straight line ways, Add isCircular() test..
Merge pull request #2194 from bhousel/bhousel-operations

Improvements to circularize action