MSC2191: Markup for mathematical messages (#2191)
* add proposal for using LaTeX for maths display
* rename to match MSC number
* change title
* update based on feedback
* up to clients how to deal with potentially-dangerous commands
* fix typo
Co-authored-by: Travis Ralston <travpc@gmail.com>
* small typo fix
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Co-authored-by: Travis Ralston <travpc@gmail.com>
Co-authored-by: Andrew Morgan <1342360+anoadragon453@users.noreply.github.com>
