Add [] and new constructor to arrays::vector

Goal :  make vector ressemble more to std::vector for generic programming.

- [] is perfectly forwarded to () for any argument.
- constructor vector (size, init_value).
- added a new little test vector_brack for this.

- now vector and std::vector have in common :
  - construction
  - resize()
  - size()
  - STL iterator
  - [] for random access.

-> next step to add cross construction with factories.
mc_generic : reorder some member construction

- as warned by clang...
- also start to clean the is_fine and add_move syntax which is a mess...