mxnet.io docs not rendering correctly

[aaronmarkham]

Description

Some tech debt from the beta site, or maybe some docstring issue... but mxnet.io doesn't look right. https://mxnet.apache.org/api/python/docs/api/mxnet/io/index.html

Mentioned here: https://github.com/apache/incubator-mxnet/issues/13804#issuecomment-452498757

Creating a specific issue to track this.