Deprecate valgrind wrapper

See merge request !2148

Using valgrind works fine without manually setting things. This was previously used to check some uninitialized values. However, we should never have uninitialized values anyway, so instead such a code should be improved.

[doxygen] exclude tests from doxygen to reduce doxygen size and runtime

Closes #887

See merge request !2141

Feature/navier stokes darcy convtest

See merge request !2128

[test] Use python3 for test wrappers

See merge request !2138

[cmake] Require CMake 3.13

See merge request !2136

* based on Schneider et al. 2019:
  Coupling staggered-grid and MPFA finite volume methods for
  free flow/porous-medium flow problems

Export element type  in FV element geometry

See merge request !2132

Fix/staggered upwindfluxvars

See merge request !2133

cleanup/staggeredupwindfluxvars ifconstexpr

See merge request !2127

[freeflow][staggeredupwindfluxvars] reduce the doLateralMomentumUpwinding_ functions with if constexpr

[freeflow][staggeredupwindfluxvars] reduce the getLateralUpwindingMomental_ functions with if constexpr

[freeflow][staggeredupwindfluxvars] reduce the getFrontalUpwindingMomenta_ functions with if constexpr

[freeflow][staggeredupwindfluxvars] reduce the doFrontalMomentumUpwinding_ functions with if constexpr

[cleanup] Remove unused typedefs

See merge request !2124

Use Markdown for auto-generated README.md

See merge request !2121