Possible clarification and reimplementation of Ref<T> classes

[mr-mocap]

I was a bit confused by the current implementation of the ConstRef and Ref classes, so I decided to see if I could clarify your original intent.

I hated to "mess up" the simplicity of the original classes, but I think I've codified what you were trying to do.

I'm hoping you will find this useful enough to merge into your repo.

[ArthurSonzogni]

Thanks! I like it!
I would like to make some small tweaks, but other it looks good to me.
I am quite busy at the moment, so please expect some delays.

[mr-mocap]

Excellent!

I was going to make some more changes to the StringRef and ConstStringRef classes, mainly seeing if I could make it a variant of a std::string and a std::string_view, as this also seems to be in the spirit of either wanting to initialize with a std::string or a hard-coded const char * string ("like this"). In this way, only an immutable string_view would mostly be passed around, which is really lightweight.

Don't worry about immediate responses, as I prefer quality over most other things. This may take some back and forth to really get it polished.

[ArthurSonzogni]

• I removed the c++20 check in example, because we are already using it.
• I added operator= for Ref.
• I removed some std::move when clang-tidy suggested it was not useful.
• I simplified some things.

Does it looks good to you?

[mr-mocap]

It looks good so far.
I have changed the implementation of ConstStringRef on my side, but I cannot figure out how to get that change into this pull request.
Perhaps I should just make another pull request after this closes.

[mr-mocap]

Found out how!
Try this out...

[ArthurSonzogni]

Thanks!
I think you overrode my last change. I will push again what I did, and if you think there are something to tweak, I will let you publish another PR.