When ``False``, the ``autosummary_ignore_module_all`` option adds
members to the module's members entry that will be used for autodoc,
but otherwise ignores it. As such, if a class is available in the 
``__all__``, it won't be generated.

This commit aims to extend the ``__all__`` handling not only to
members, but also to corresponding attribute types (function,
classes, exceptions, modules)

The ``imported_members`` option is set to ``True`` if the object has
an ``__all__`` member and ``autosummary_ignore_module_all`` is ``False``