Update documentation style & fix room version heading order (#3683)

* Update documentation style & fix room version heading order

Also add a missing signing key section to v6.

This additionally contains various edits to the fragments to have them make a little bit more sense in context.

Finally, this updates various aspects of the documentation style which haven't previously been considered - they're added here considering we're in the area.

* changelog

* enhanced changelogs

* Minor wording adjustments

* Apply suggestions from code review

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

content/rooms/v9.md

@@ -90,13 +90,9 @@ following considerations.
 The following sections have not been modified since v8, but are included for
 completeness.
 
-### State resolution
+### Handling redactions
 
-{{% rver-fragment name="v2-state-res" %}}
-
-### Authorization rules
-
-{{% rver-fragment name="v8-auth-rules" %}}
+{{% rver-fragment name="v3-handling-redactions" %}}
 
 ### Event IDs
 
@@ -106,9 +102,13 @@ completeness.
 
 {{% rver-fragment name="v4-event-format" %}}
 
-### Handling redactions
+### Authorization rules
 
-{{% rver-fragment name="v3-handling-redactions" %}}
+{{% rver-fragment name="v8-auth-rules" %}}
+
+### State resolution
+
+{{% rver-fragment name="v2-state-res" %}}
 
 ### Canonical JSON