Exporting structured grid into xdmf format

[parismulye]

I feel that this could be an interesting feature to have:

Why:

• Consider a case where the mesh is basically a 3D image with millions of voxels
• In this case, storing the connectivity matrix (cells) can be very expensive (in terms of storage) and is redundant

Idea:

• An xdmf file that uses a structured grid format
• Later on one can use this same format and inject the solution into the mesh (in a binary file for example)

Example:
This is a sample example that I built that can be read into paraview.

• prep.bin is some cell data)
• it is an xdmf file (but I changed the extension to .txt for uploading)

prep.txt