Playground for Dune wrapper around GridFormat::Writer

Clone this module with the flag --recursive in order to bring in the GridFormat library.

Contains a single executable (requires dune-functions):

make test_io
./test_io  # (optional) pass number of desired cells per direction as argument

TODO:

• For higher-order output, the higher-order grid is currently fully built upon construction of the writer, and an update mechanism (e.g. when the grid changes) is currently not exposed. One could think about building and destroying this grid when an actual write is performed, using the update and clear functions of the GridFormat::Dune::LagrangePolynomialGrid.
• Add Dune::GridFactory wrappers to the traits to facilitate reading in Dune grids from grid files with the GridFormat reader.