[CMake] Require at least CMake 3.0
This is a trial balloon to see the fall out. If nobody complains for dune-grid-howto, we can make this change for all core modules.
See FS#1619.
This is a trial balloon to see the fall out. If nobody complains for dune-grid-howto, we can make this change for all core modules.
See FS#1619.