This unifies the doxygen headers. If the (doxygen) header is not
starting with \file, the following documentation is attributed to a
different entity resulting is multiple copyright blocks and the like in
the doxygen's html files.

Eliminate two single-line functions.

The vector has same structure as for the monolithic
case.

The vector has same structure as for the monolithic
case.

Semantically identical to vector of references.

Pass process_id to FEM::assemble calls.

If only file name is specified it causes a warning
about the name not to be specific enough if there is
another file with the same name, e.g.:

the name `IdealGasLaw.h' supplied as the second argument
in the \file statement matches the following input
files: ogs/MaterialLib/Fluid/Density/IdealGasLaw.h
ogs/MaterialLib/MPL/Properties/IdealGasLaw.h
Please use a more specific name by including a (larger)
part of the path!

From now on only \file w/o a name or a full path will
be allowed.

find -type f | xargs sed -i 's%\(\\file\).*%\1%'

Same as in the getPreviousLocalSolutions().

for flexibility in coupling.

for the staggered scheme.

about getting the local solutions of an element.

Clang format run on near-the-header lines.

Happy New Year

 from the two classes of coupled term.

[Coupling] Changed the members of the coupled term,

 which only contains the solutions of the coupled equations.

added more documentations about the staggered scheme

coupled terms.