GridFormat v0.2.0

Features

• Documentation: the available file formats are now listed as a separate Doxygen group.
• CI: for PRs, only the tests affected by changes in the PR are built and run in order to speed up the workflows.
• Field: Field::export now accepts r-values, which will be used to populate the values and return them again. Thus, one can now write const auto values = field.export_to(std::vector<double>{}), where auto will be std::vector<double>.
• Traits: added a GridFactoryAdapter for Dune::GridFactory to the dune traits to facilitate exporting read grids into dune grids.