Merge branch 'feature/discrete-functions' into 'develop'

src/algebra/BiCGStab.hpp

src/algebra/CG.hpp

src/algebra/TinyVector.hpp

src/algebra/Vector.hpp

src/language/modules/MathFunctionRegisterForVh.cpp

src/language/modules/MathModule.cpp

src/language/modules/SchemeModule.cpp

...language/utils/EmbeddedIDiscreteFunctionMathFunctions.cpp

...language/utils/EmbeddedIDiscreteFunctionMathFunctions.hpp

src/mesh/GmshReader.cpp

src/mesh/MeshData.hpp

src/mesh/MeshNodeBoundary.hpp

src/scheme/AcousticSolver.cpp

src/scheme/CMakeLists.txt

src/scheme/DiscreteFunctionP0.hpp

src/scheme/PerfectGas.cpp

src/scheme/PerfectGas.hpp

src/utils/Messenger.hpp

src/utils/PugsUtils.hpp

tests/test_BiCGStab.cpp