Update prop358 with comments from #325.

Closes #325

See merge request !367

consensus-formats: formatting of router items (and finish server-desc items)

See merge request !330

New Proposal 361: Onion Association SANs In Certificates (OASIC)

See merge request !368

Author: Paul Syverson

Closes #325.

Prompted by
  !330 (comment 3148379)

 * In identity-ed25519, say which key is certified by what.
 * In router-sig-ed25519 say that it's the same KP_relaysign_ed

Prompted by
  !330 (comment 3148381)

As per
  !330 (comment 3148376)

Prompted by
  !330 (comment 3148373)

As per
  !330 (comment 3148371)

This branch is long enough now.

And state the encoding too.

I found the previous description confusing in several ways.  This
description is what I infer must be the case.

These are at the end of the descriptor.  Putting them at the end of
the document too is much better.

Put the information in order, and use a bulleted list.

Use the simple declarative mood.  Name the signing key rather than
referencing an item it's in.

These two items were smooshed together in a code block quote.