MSC3821: Update the redaction rules, again (#3821)
* Start an MSC2176 2.0
* Remove scary warning about unstable implementation
* Update spec links
* Apply suggestions from code review
Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>
* Rewrite words into order that sense make
* Update intro & unstable prefix history
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Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>