Implement `Norm` and `Dot` for `DVec`.
Implement `Norm` and `Dot` for `DVec`.

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