DOC: Fix warning for PyArray_MapIterNew.

[liang3zy22]

Fix two warnings about missing reference . The two warnings are for PyArray_MapIterNew.

[rossbar]

I think the main question here is whether PyArray_MapIterNew is intended to be public C-API. From the references in the Advanced Indexing doc which you pointed out, it seems plausible that it is intended to be public. @seberg / @charris any thoughts on this one?

If this is a public function then this change LGTM, with perhaps a slight update to the c:function description to be a little more specific.

[seberg]

I would like to make it proper private and see if someon complains, the only known user was theano, which I consider historic at this point. For practically everything getting it right and fast is difficult, so using advanced indexing or ufunc.at is better anyway (including the theano usecase).

Keeping it public makes the struct a big mess, so I have doubts anyone figured out how to use it the fast way.

[rossbar]

Thanks @seberg ! Given that, @liang3zy22 I think a better approach would be to convert the references to PyArray_MapIterNew to unlinked objects (e.g. use PyArray_MapIterNew instead).

[rossbar]

Rendered docs look good, in it goes. Thanks @liang3zy22 !