message: elle.as_range: expose the iterator types for Boost
diff: @@ -9,6 +9,8 @@ namespace elle
  template <typename It>
  struct range
  {
  + using iterator = It;
  + using const_iterator = It;
  It begin() const { return _begin; }
  It end() const { return _end; }
  It _begin, _end;
  