critic markup integration

As a collaborative tool, it could be great that HackMD | CodiMD implement collaborative modification provides by critic markup, as described [here](https://github.com/CriticMarkup/CriticMarkup-toolkit#welcome-to-the-criticmarkup-toolkit), at least the five basic critic marks:
>Addition {++ ++}
>Deletion {-- --}
>Substitution {~~ ~> ~~}
>Comment {>> <<}
>Highlight {== ==}{>> <<}

That could be a huge enhancement for collaborative writing…