Merge branch 'develop' into feature/discontinuous-galerkin

.gitignore

.gitlab-ci.yml

.gitlab-ci/clang10-mpi-debug.yml

.gitlab-ci/clang10-mpi-release.yml

.gitlab-ci/gcc10-mpi-coverage.yml

.gitlab-ci/gcc10-mpi-debug.yml

.gitlab-ci/gcc10-mpi-release.yml

.gitlab-ci/gcc10-seq-coverage.yml

.gitlab-ci/gcc10-seq-release.yml

CMakeLists.txt

packages/PEGTL/src/test/pegtl/file_äöü𝄞_data.txt

src/CMakeLists.txt

src/algebra/BiCGStab.hpp

src/algebra/CG.hpp

src/algebra/CMakeLists.txt

src/algebra/CRSMatrix.hpp

src/algebra/LinearSolver.cpp

src/algebra/LinearSolver.hpp

src/algebra/LinearSolverOptions.cpp

src/algebra/LinearSolverOptions.hpp