- simpler to write for sampled cutting planes etc.
  For example,

      slice
      {
          type        cuttingPlane;
          point       (0 0 0);
          normal      (0 0 1);
          interpolate true;
      }

  instead of

      slice
      {
          type        cuttingPlane;
          planeType   pointAndNormal;
          pointAndNormalDict
          {
              point   (0 0 0);
              normal  (0 0 1);
          }
          interpolate true;
      }

STYLE: add noexcept to some plane methods