Adding segments views.

src/Benchmarks/SpMV/spmv.h

src/TNL/Containers/Segments/CSR.h

src/TNL/Containers/Segments/CSR.hpp

src/TNL/Containers/Segments/CSRView.h

src/TNL/Containers/Segments/CSRView.hpp

src/TNL/Containers/Segments/Ellpack.h

src/TNL/Containers/Segments/Ellpack.hpp

src/TNL/Containers/Segments/EllpackView.h

src/TNL/Containers/Segments/EllpackView.hpp

src/TNL/Containers/Segments/SlicedEllpack.h

src/TNL/Containers/Segments/SlicedEllpack.hpp

src/TNL/Containers/Segments/SlicedEllpackView.h

src/TNL/Containers/Segments/SlicedEllpackView.hpp

src/TNL/Containers/Segments/details/CSR.h

src/TNL/Containers/Segments/details/Ellpack.h

src/TNL/Containers/Segments/details/SlicedEllpack.h

src/TNL/Matrices/SparseMatrix.h

src/TNL/Matrices/SparseMatrix.hpp

src/UnitTests/Containers/Segments/SegmentsTest.hpp

src/UnitTests/Matrices/SparseMatrixTest_Ellpack_segments.h