message: Make submodules the preferred names, except for modules, they should prefer the root.
  Prefer `tf.submodule.Symbol` to `tf.Symbol`.
  When the object is a module, then prefer
  `tf.submodule` over `tf.package.submodule` so that `tf.submodule.Symbol` finds `tf.submodule`.
diff: @@ -194,10 +194,11 @@ class DocGeneratorVisitor(object):
  contrib_score = 1
  while parts:
  - parts.pop()
  container = self._index['.'.join(parts)]
  if tf_inspect.ismodule(container):
  break
  + parts.pop()
  +
  module_length = len(parts)
  if len(parts) == 2:
  # `tf.submodule.thing` is better than `tf.thing`
  