add MotionMat I/F

  initWithSize:bgr:
  copyTo:mask:
  copyTo:
add/remove I/F

  add MotionCV I/F
    .circle
    .rectangle
    .split
    .distanceTransform

  add MotionMat I/F
    #channels

  remove MotionMat I/F
    .copyTo: (to crash)