message: das.named: Add named agruments mapping.
diff: @@ -297,6 +297,15 @@ namespace elle
  return f(find<Index, Formal, Args...>::get(
  defaults, std::forward<Args>(args)...)...);
  }
  +
  + template <typename Default, typename F, typename ... Args>
  + static
  + auto
  + map(Default& defaults, F const& f, Args&& ... args)
  + {
  + return std::make_tuple(find<Index, Formal, Args...>::get(
  + defaults, std::forward<Args>(args)...)...);
  + }
  };
  template <typename F, typename ... Args>
  @@ -307,6 +316,14 @@ namespace elle
  this->defaults, f, std::forward<Args>(args)...);
  }
  + template <typename ... Args>
  + auto
  + map(Args&& ... args) const
  + {
  + return Call<std::make_index_sequence<sizeof ... (Formal)>>::map(
  + this->defaults, std::forward<Args>(args)...);
  + }
  +
  template <typename Arg>
  struct print_prototype
  {
  