Document C++ code and update README with basic installation and usage instructions.

.gitlab-ci.yml

CHANGELOG.md

README.md

dune/copasi/CMakeLists.txt

dune/copasi/common/CMakeLists.txt

dune/copasi/common/coefficient_mapper.hh

dune/copasi/common/enum.hh

dune/copasi/common/muparser_data_handler.hh

dune/copasi/common/parameter_tree_check.hh

dune/copasi/common/pdelab_expression_adapter.hh

dune/copasi/common/tiff_grayscale.hh

dune/copasi/finite_element/CMakeLists.txt

dune/copasi/finite_element/dynamic_local_basis.hh

dune/copasi/finite_element/dynamic_local_coefficients.hh

dune/copasi/finite_element/dynamic_local_finite_element.hh

dune/copasi/finite_element/dynamic_local_interpolation.hh

...si/finite_element/multidomain_local_finite_element_map.hh

dune/copasi/grid/CMakeLists.txt

dune/copasi/grid/multidomain_entity_transformation.hh

dune/copasi/grid/multidomain_gmsh_reader.hh