Mnorm

mnorn and globalnorm have been writen to compute respectively matricial and vectorial norms  with dynamic or static choice of the formula used.

norm which mimicks the matlab behaviour calls these two accordingly, but is no more called directly by any
nt2 functor.

Definition and mode of choice of the norms can be seen in dox tables situated in globalnorm.hpp mnorm.hpp and norm.hpp
this files coudl live into sdk or base instead of placeholders. As of now, this makes a dependencies between norm module and core.placeholders which is un-needed IMHO.