Merge branch 'string' into 'develop'

src/Benchmarks/BLAS/tnl-benchmark-blas.h

src/Benchmarks/Benchmarks.h

src/Benchmarks/DistSpMV/tnl-benchmark-distributed-spmv.h

src/Benchmarks/HeatEquation/tnlTestGrid2D.h

src/Benchmarks/LinearSolvers/tnl-benchmark-linear-solvers.h

src/Examples/StringExample.cpp

...les/transport-equation/transportEquationProblemEoc_impl.h

src/Python/pytnl/tnl/String.cpp

src/TNL/Containers/MultiVector1D_impl.h

src/TNL/Containers/MultiVector2D_impl.h

src/TNL/Containers/MultiVector3D_impl.h

src/TNL/Containers/MultiVector4D_impl.h

src/TNL/Containers/StaticArray1D_impl.h

src/TNL/Containers/StaticArray2D_impl.h

src/TNL/Containers/StaticArray3D_impl.h

src/TNL/Containers/StaticArray_impl.h

src/TNL/Containers/StaticVector1D_impl.h

src/TNL/Containers/StaticVector2D_impl.h

src/TNL/Containers/StaticVector3D_impl.h

src/TNL/Containers/StaticVector_impl.h