Order of the elements in JSON object

[amirhosseindavoody]

This is not an issue or the bug, but something that I noticed while using your library and I think it should be included in the documentation just for the sake of completeness.

I have noticed that when a JSON structure is created the order in which the elements are printed is in alphabetical order of name of properties. It would be nice to include this somewhere in the documentation of the library.

[nlohmann]

It's in the README: https://github.com/nlohmann/json#notes (last note).

[nlohmann]

To be fixed with #2258.