Add possiblity to create ".pvd"-files in vtk-writer
Currently, the files that are written in pystencil's vtk-writer are stored as vtkImageData (.vti) only. It would be great if the vtk-writer was able to create a file in ParaView Data format (.pvd) which contains the path to each .vti-file and the (LBM) time step at which the file was written.
In ParaView, "time" would then actually represent the (LBM) time step instead of being equal to the index, i.e., number of the loaded ".vti"-file.