addNewFaces (eyeVertex, horizon) {
    this.newFaces = []
    let firstSideEdge, previousSideEdge
    for (let i = 0; i < horizon.length; i += 1) {
      const horizonEdge = horizon[i]
      // returns the right side edge
      const sideEdge = this.addAdjoiningFace(eyeVertex, horizonEdge)
      if (!firstSideEdge) {
        firstSideEdge = sideEdge
      } else {
        // joins face.getEdge(1) with previousFace.getEdge(0)
        sideEdge.next.setOpposite(previousSideEdge)
      }
      this.newFaces.push(sideEdge.face)
      previousSideEdge = sideEdge
    }
    firstSideEdge.next.setOpposite(previousSideEdge)
  }
Adds horizon.length faces to the hull, each face will be 'linked' with the
horizon opposite face and the face on the left/right

@param {Vertex} eyeVertex
@param {HalfEdge[]} horizon - A chain of half edges in ccw order