prop329: Add section numbers

See merge request !340

Yes, there are two section "2.4"s and a missing section "6" to match the
original txt document.

Assign mnemonic names to subprotocol versions.

Closes #252

See merge request !251

See discussion in #252.

Prop354 relaxed restrictions

See merge request !338

prop329: Format as markdown

See merge request !336

Reserve consensus method 35 for happy families.

See merge request !335

prop321: Clean up naming a bit.

See merge request !334

Co-authored-by: Alexander Hansen Færøy <ahf@torproject.org>

Rename "family-keys" to "family-ids":
the entries here are arbitrary strings,
and aren't necessarily convertible to keys.

Introduce "family list" to mean "a legacy list of family members".

Add an "ed25519:" prefix to family ids derived from family certs.

prop321: More clarifications and cleanups

See merge request !333

- It's okay to start updating authorities on the early side.
- We should test the whole pipeline in chutney before we release it.

Notably, this feature indicates that we _accept_
happy families; not that we _generate_ them.

Reserve names and values for prop321 (happy families)

See merge request !332

In order to produce compatible implementations,
we need to document the key name,
the certificate type code,
and a subprotocol version.

Happy families edits and clarifications

See merge request !331

(Mike reminded me of this on a pad discussion.)