+ Put laters around heap assumptions in heap.v
- A few fixes in substitutions.v :
   + Replaced csimpl by cbn [subst_l subst'] in simpl_subst for
     better performances
   + Enforce the right order for rewriting do_subst
   + added list constructors instances for WSubstL
   + Fixed the hint extern for WSubst Rec
- Compatibility with new intro patterns
- Better notations for language constructs : function parameters are
  listed within []
- Proved memcpy. TODO : improve perforamnces (time and memory).