Changelog updates
Rename: RelativePosition.x --> .right
Rename: RelativePosition.y --> .down
Pixels.minus()
Position.minus()
Size.minus()
RelativePosition.down()
RelativePosition.up()
RelativePosition.toString() renders all 4 directions correctly
ElementEdge.minus() can take an element size
INTEGRATE: Can subtract ElementSize from ElementEdge

* dev:
  ElementEdge.minus() can take an element size
  RelativePosition.toString() renders all 4 directions correctly
  RelativePosition.up()
  RelativePosition.down()
  Size.minus()
  Position.minus()
  Pixels.minus()
  Rename: RelativePosition.y --> .down
  Rename: RelativePosition.x --> .right
  Changelog updates