Update to QR factorization interface :

Changed underlying architecture to make direct calls to lapack kernels making qr_result obsolete.
QR function API is now fully matlab compliant for dense matrix. For this purpose a new system of
policy hierarchies has been setup globally.

Various details functions were added to handle all the cases that occurs in qr implementation.
Benchmarks for lu and qr calls to make sure that the overhead generated by nt2
is not significant compared to direct lapack calls.