src/sankeyCircular.js
function ascendingBreadth (a, b) {
    if (a.partOfCycle === b.partOfCycle) {
      return a.y0 - b.y0
    } else {
      if (a.circularLinkType === 'top' || b.circularLinkType === 'bottom') {
        return -1
      } else {
        return 1
      }
    }
  }
function ascendingBreadth (a, b) {
    if (a.partOfCycle === b.partOfCycle) {
      return a.y0 - b.y0
    } else {
      if (a.circularLinkType === 'top' || b.circularLinkType === 'bottom') {
        return -1
      } else {
        return 1
      }
    }
  }
sort nodes' breadth (ie top to bottom in a column) if both nodes have circular links, or both don't have circular links, then sort by the top (y0) of the node else push nodes that have top circular links to the top, and nodes that have bottom circular links to the bottom