ElementEdge.toString() no longer takes optional parameter
ElementEdge.plus() and ElementEdge.minus()
ElementEdge.diff() works with ElementPosition
ElementPosition.diff() works with ElementEdge()
INTEGRATE: ElementEdge.plus() and .minus()

* dev:
  ElementPosition.diff() works with ElementEdge()
  ElementEdge.diff() works with ElementPosition
  ElementEdge.plus() and ElementEdge.minus()
  ElementEdge.toString() no longer takes optional parameter