first draft of mpi
mpi for arrays
mpi for arrays pass first tests.

- removed the basic_array class, it is not really useful,and also some internal small classes
- code is clearer.
- pass tests on arrays :
   - scatter, gather on array<long,2> array<complex,2>, etc...
   - broadcast
- split in several files for readibility
- coded the std::vector aloong the same line, but not tested.

- TODO : more tests :
  - reduce
 - 1d arrays, just to be sure.
 - tests, tests, tests...
 - generic mecanism
moving tests and details
first test of generic case ok
fix mpi/vector, added test