Revise our code to only call Request.Namespace() if a namespace
*should* be present. For root scoped resources, namespace should
be ignored. For namespaced resources, it is an error to have
Namespace=="".
Create a unified Builder object for working with files, selectors,
types, and items that makes it easier to get multi-object functionality.
Supports all of the behaviors previously in resource.go, but with
additional flexibility to allow multi-type retrieval and access, directories,
URLs, nested objects, and lists.
