arrays: length of domain corrected for &&
h5: add a parent in group

- add a parent in the group, to allow iteration on group
elements
- normally in h5, one needs to have the parent group and the name
of the group to iterate on its elements.
- added a parent (possibly empty) to get a simply syntax to
get the element of a group...
tuple tools : add reverse for a tuple...

- add in std:: the reverse to be able to apply the algorithms on a
  reversed tuple
- overloaded std::get, std::tuple_size for this
- added tests.
array: add a contructor for reshaping temporary

- add a constructor from indexmap and storage &&,
- used when reshaping a temp. array.