feat(builders): request type handling part 1

Now we will generate proper resoure methods builder calls to instaniate
the more or less valid method builders.

However, it doesn't compile yet, and the 'to_parts()' method on
resources is still missing.

gen/youtube3/src/cmn.rs

@@ -21,7 +21,7 @@ pub trait Resource: MarkerTrait {}
 pub trait ResponseResult: MarkerTrait {}
 
 /// Identifies types which are used in API requests.
-pub trait RequestResult: MarkerTrait {}
+pub trait RequestValue: MarkerTrait {}
 
 /// Identifies types which are only used as part of other types, which 
 /// usually are carrying the `Resource` trait.