support for 31/32/63/64-bit integers in extracted code

All files are extracted to the target repository, even those
corresponding to files from the Why3 standard library.
Some of these files may be empty (e.g. ref__Ref.ml) when everything
is overridden by the OCaml driver. You can ignore these files when
compiling the extracted OCaml code.

everything is contained in the driver (ocaml.drv)
with possible references to OCaml modules contained in why3extract.cma
(currently why3__Prelude, why3__BigInt, why3__Map)

in particular, consistency of ArrayPermut is now ensured

(that is, using number of occurrences)
No more definition of permutation using inductive predicates.
Impacts array.ArrayPermut; proof sessions updated.
Coq realizations for map.Occ and map.MapPermut;
proof session for array.ArrayPermut in progress

Problem: lambda is not extracted into a fun ... -> ...