Update client-server API endpoints to move from r0 to v3 (plus whitespace fixes) (#3421)

* Blind find & replace all on client major version -> v3

* Fix up bad replacements

* Fix anchors for r0->v3

* Changelog

data/api/client-server/message_pagination.yaml

@@ -19,7 +19,7 @@ host: localhost:8008
 schemes:
   - https
   - http
-basePath: /_matrix/client/%CLIENT_MAJOR_VERSION%
+basePath: /_matrix/client/v3
 consumes:
   - application/json
 produces:
@@ -55,7 +55,7 @@ paths:
             or from an `end` token returned by a previous request to this endpoint.
 
             This endpoint can also accept a value returned as a `start` token
-            by a previous request to this endpoint, though servers are not 
+            by a previous request to this endpoint, though servers are not
             required to support this. Clients should not rely on the behaviour.
           required: true
           x-example: "s345_678_333"