Merge branch 'fix/codespell' into 'master'

README.md

bin/extract_as_new_module.py

bin/installdumux.py

bin/util/moduleinfo.py

doc/doxygen/pages/external-libs.md

doc/doxygen/pages/input-output.md

doc/doxygen/pages/parameters.md

dumux/adaptive/griddatatransfer.hh

dumux/assembly/partialreassembler.hh

dumux/common/math.hh

dumux/common/properties.hh

dumux/common/spline.hh

...cretization/staggered/freeflow/staggeredgeometryhelper.hh

...discretization/staggered/freeflow/subcontrolvolumeface.hh

dumux/freeflow/shallowwater/indices.hh

dumux/io/gnuplotinterface.hh

dumux/io/grid/gridmanager_alu.hh

dumux/io/grid/porenetwork/gridmanager.hh

dumux/io/json/json.hpp

dumux/material/fluidsystems/brine.hh