Merge branch 'MC/mpi_support' into devel

CMakeLists.txt

contrib/sgr

doc/changelog.md

doc/lua_api.md

include/common/eigen.h

include/common/gpu_support.hpp

include/common/mpi_helpers.h

include/common/point.hpp

include/common/types.h

include/libgmshdg/connectivity.h

include/libgmshdg/entity.h

include/libgmshdg/entity_data.h

include/libgmshdg/gmsh_io.h

include/libgmshdg/kernels_cpu.h

include/libgmshdg/kernels_gpu.h

include/libgmshdg/param_loader.h

include/libgmshdg/physical_element.h

include/libgmshdg/reference_element.h

include/libgmshdg/silo_output.hpp

include/maxwell/maxwell_common.h