Revisions to prop346 and accompanying spec tweaks

This MR cleans up some issues in proposal 346.

It also documents the numeric values for our protocol types, and tweaks/adjusts some descriptions of unimplemented cruft.

Part of #317.

added 6h of time spent

assigned to @nickm

requested review from @ahf

I think I will need @dgoulet in on this one -- he is the person who has touched this the most I think.

@dgoulet Can you grab this one?

requested review from @dgoulet and removed review request for @ahf

approved this merge request

mentioned in commit fe59a628

merged