fix(resource): now with flattened activities

That way, we don't have recursive method builders, but instead
flatten the hierarchy. In our case, this is easier and means
less to type. E.g.

`hub.user().message().import(...)` now is
`hub.user().message_import(...)`

In go it would look like this though
`hub.user.messages.import(...)
which is neater.

We will never have that though, as it will initialize a massive amount
of data right on the stack, even though only some of it is ever used
... .

gen/youtube3/README.md

@@ -54,13 +54,13 @@ let r = hub.resource().activity(...).doit()
 Or specifically ...
 
 ```ignore
-let r = hub.live_broadcasts().control(...).doit()
-let r = hub.live_broadcasts().insert(...).doit()
-let r = hub.live_broadcasts().list(...).doit()
-let r = hub.live_broadcasts().transition(...).doit()
-let r = hub.live_broadcasts().update(...).doit()
-let r = hub.live_broadcasts().delete(...).doit()
-let r = hub.live_broadcasts().bind(...).doit()
+let r = hub.live_broadcast().control(...).doit()
+let r = hub.live_broadcast().insert(...).doit()
+let r = hub.live_broadcast().list(...).doit()
+let r = hub.live_broadcast().transition(...).doit()
+let r = hub.live_broadcast().update(...).doit()
+let r = hub.live_broadcast().delete(...).doit()
+let r = hub.live_broadcast().bind(...).doit()
 ```
 
 The `resource()` and `activity(...)` calls create [builders][builder-pattern]. The second one dealing with `Activities`