Adding the Lax-Fridrichs scheme.

examples/navier-stokes/Makefile

examples/navier-stokes/navierStokesSolver_impl.h

examples/navier-stokes/share/examples/cavity

src/CMakeLists.txt

src/config/parse.cc

src/config/tnlConfigDescriptionParser.h

src/config/tnlConfigDescriptionParser.ih

src/config/tnlConfigDescriptionParser.y

src/config/tnlConfigDescriptionParserbase.h

src/config/tnlConfigDescriptionScanner.cpp

src/config/tnlConfigDescriptionScanner.l

src/implementation/CMakeLists.txt

src/implementation/core/mfilename.cpp

src/implementation/core/mpi-supp.cpp

src/implementation/core/tnlLogger.cpp

src/implementation/core/tnlString.cpp

src/implementation/core/tnlTimerCPU.cpp

src/implementation/core/tnlTimerRT.cpp

src/implementation/schemes/CMakeLists.txt

src/implementation/schemes/euler/CMakeLists.txt