Autodoc generates reST code that uses raw `:obj:` and `:class:` xrefs to
refer the classes and types. But they're fragile because they assume
the primary_domain=='py'.
This adds `:py:` prefix to these xrefs to make them robust.
autodata and autoattribute directives does not show right-hand value of
the variable if its docstring contains ``:meta hide-value:`` in
info-field-list.
A custom type defined by typing.NewType was rendered as a function
because the generated type is a function having special attributes.
This renders it as a variable.
Note: The module name where the NewType object defined is lost on
generating it. So it is hard to make cross-reference for these custom
types.
