small modification for "_" functions
tiny modification of dssmatrix::zero.
the type of Line and line object of dssmatrix were changed to std::vector.
tiny modification for streatch and expand functions
3D classes were all deleted.
*a tiny mistake on dssmatrix-misc.hpp was revised.
*small modification for small classes.
*modification of small matrix classes
*modification of small matrices.
*Small matrix and vector classes were added. They are so far from completion.
