message: das.Symbol: Pretty print effective arguments.
diff: #include <string>
  +#include <elle/printf-fwd.hh>
  +
  namespace elle
  {
  namespace das
  @@ -68,6 +70,14 @@ namespace elle
  {
  return S::name();
  }
  +
  + friend
  + std::ostream&
  + operator<<(std::ostream& out, Effective const& e)
  + {
  + elle::fprintf(out, "%s = %s", e.name(), e.value);
  + return out;
  + }
  };
  template <typename E>
  