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/inviting.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:
@@ -36,7 +36,7 @@ paths:
         *Note that there are two forms of this API, which are documented separately.
         This version of the API requires that the inviter knows the Matrix
         identifier of the invitee. The other is documented in the*
-        [third party invites section](/client-server-api/#post_matrixclientr0roomsroomidinvite-1).
+        [third party invites section](/client-server-api/#post_matrixclientv3roomsroomidinvite-1).
 
         This API invites a user to participate in a particular room.
         They do not start participating in the room until they actually join the