Matrix: more implementations and improved benchmarking
Matrix: more implementations and improved benchmarking

* use int for iteration variables
* new Matrix default ctor which inits the data to zero
* fix indenting
* additional scalar implementation which uses blocking
* improve benchmark code and output to generate a nice table

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

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