message: Simplify and add some references
diff: @@ -8604,6 +8604,7 @@ int ConvertToVTKOrdering(int idx_in, int ref, Geometry::Type geom)
  return idx_in;
  case Geometry::SQUARE:
  {
  + // Cf: https://git.io/JvZLT
  int i = idx_in % n;
  int j = idx_in / n;
  // Do we lie on any of the edges
  @@ -8630,6 +8631,7 @@ int ConvertToVTKOrdering(int idx_in, int ref, Geometry::Type geom)
  }
  case Geometry::CUBE:
  {
  + // Cf: https://git.io/JvZLe
  int i = idx_in % n;
  int j = (idx_in / n) % n;
  int k = idx_in / (n*n);
  @@ -8777,11 +8779,8 @@ void Mesh::PrintVTU(std::ostream &out, int ref, bool binary,
  for (int iel = 0; iel < GetNE(); iel++)
  {
  Geometry::Type geom = GetElementBaseGeometry(iel);
  - int geom_dim = Geometry::Dimension[geom];
  - int ni = ref+1;
  - int nj = geom_dim > 1 ? ref+1 : 1;
  - int nk = geom_dim > 2 ? ref+1 : 1;
  - int nnodes = ni*nj*nk;
  + RefG = GlobGeometryRefiner.Refine(geom, ref, 1);
  + int nnodes = RefG->RefPts.GetNPoints();
  local_connectivity.SetSize(nnodes);
  for (int i=0; i<nnodes; ++i)
  {
  @@ -8844,6 +8843,7 @@ void Mesh::PrintVTU(std::ostream &out, int ref, bool binary,
  Array<int> &RG = RefG->RefGeoms;
  uint8_t vtk_cell_type = 5;
  + // VTK element types defined at: https://git.io/JvZLm
  switch (geom)
  {
  case Geometry::POINT:
  