generic implementation of QR decomposition
generic implementation of QR decomposition

But static matrices can't use it yet, they need to implement the
Row/Col slicing traits.

mbStavola/nalgebra,tempbottle/nalgebra,sebcrozet/nalgebra,tikue/nalgebra,tomaka/nalgebra,ProtectedMode/nalgebra,jaredly/nalgebra,sebcrozet/nalgebra