A first (non-working yet) implementation of composites.
Introduced the internal_data level for references & private data + major
fixes everywhere.
Restore to original Julien's behavior (ctor).
Fix bootstrap for consistency with the other generated elements
Basic compilation scheduling.
Merge pull request #15 from StephaneSeyvoz/composite

Composite generation + internal_data superclass + compilation + fix
Merge pull request #11 from Mind4SE/master

Keeping up-to-date