consensus-formats: formatting of router items up to and excluding `s`

s is done in !324 (merged), so stopping this branch here.

spec/dir-spec/consensus-formats.md

@@ -582,7 +582,7 @@ or `0` for "none".
 ### `a` --- Further router address(es) (IPv6) {#item:a}
 
  * **`a`** _address_:_port_
- * At most once
+ * Any number
 
 <!-- TODO inconsistency: : here, but port separated by space in `r` -->
 
@@ -598,9 +598,8 @@ and the authority believes that
 the first advertised address is reachable.
 Any other IPv4 or IPv6 addresses should be ignored.
 
-> Current client implementations accept multiple `a` items,
-> ignore any `a` items containing IPv4 addresses,
-> and use the first IPv6 address `a` (if there is one) for IPv6.
+<!-- TODO why can this be repeated
+     if we only ever look at the first one in the server desc? -->
 
 (Only included when the vote or consensus is generated with
 consensus-method 14 or later.)