Update and Markdownify Proposal 344

I need a place to gather questions people have asked re prop#344 protocol issues that may warrant a mention or explanation inside prop#344. This is that place.

During such an update, we should also normalize the refs, and markdown it.

Here's a list:

• tor#40977 (comment 3083791)
• tor#40935 (comment 3090023)
• arti#1425 (comment 3033351)
• arti!2544 (diffs, comment 3094696)
• #226 (comment 2961244)
• Use OG Tor Design Doc terminology to motivate how the severe side channels upgrade attacks from "traffic analysis" to "traffic confirmation", or worse.
• Historical issues like .exit notation, exitpolicy abuse, and other "free route" mixnet guard discovery bugs where the application layer was also free to influence paths to attack users
• Historical path restriction issues touched on in the bridge family ticket

This description will be edited.