Matrix: compare valarray based Matrix
Matrix: compare valarray based Matrix

* new MatrixValarray class template to show an optimized valarray based
matrix implementation efficiency
* The valarray storage cannot use a single valarray because slice_arrays
are not usable for anything and const operator[] of valarray returns a
valarray COPY!
* the alternative, using Matrix for storage and valarray only for
implementing the multiplication is also implemented, but so slow that I
did not keep it enabled in the benchmark.

Signed-off-by: Matthias Kretz <372ea4eca737a13cd010ee806d4ce7b98ee71550@kde.org>

VcDevel/Vc,VcDevel/Vc,chr-engwer/Vc,chr-engwer/Vc,chr-engwer/Vc,VcDevel/Vc,VcDevel/Vc