Modernize and clarify subprotocol sections

This branch has editorial changes to improve the clarity of our description of subprotocol-based versioning in the Tor protocol. In our current vocab, we don't want to refer to "Relay=3" as a "version", since that implies that "Relay=4" is a "greater version".

It also adopts the "subprotocols are flags" section of proposal 346.

Part of #317

assigned to @nickm

changed the description

added 3 commits

• 0fada728 - Clean up misleading references to "protocol versions".
• 5d873aa9 - Add cross-references for how suprotos are published.
• 2724111d - Crosslink and improved description for required/recommended subprotos

Compare with previous version

requested review from @dgoulet

This is fantastic!

approved this merge request

mentioned in commit 673484a4

merged

mentioned in commit 7dbc9706

mentioned in issue arti#1934