arrays: add make_unit_matrix and norm2, norm2_sqr
clef: correction of macro

- a strange issue, why was it not working ?
- anyway, the separation is useless (was a try).
c14, tuples : various fixes.

- Various details (for_each_enumerate impl)
- also put all tuple stuff in tuple_tools.hpp
- add std14 namespace for usage of c++14 helper types
gf: add C++14 impl of meshes products

-  add c14 include
- the C++14 is lot more readable (due to generic lambda).
- for mesh/product.hpp -> now 2 versions (C++14 and C++11 for temporary
  backward compatibility).
lattice: clean old classes, add bz_mesh, gf on bz