[DOC] ImageRecordIter doesn't render correctly

[eric-haibin-lin]

The doc for image record io is broken. See http://mxnet.incubator.apache.org/versions/master/api/python/io/io.html#mxnet.io.ImageRecordIter

The source documentation in cpp was not changed in the past 10 months. I suspect there's some thing wrong with the doc building script (if it was changed recently by any chance).

Also, doc for LibSVMIter and CSVIter are broken, too.

@aaronmarkham @thinksanky

[aaronmarkham]

Dev builds show this as fixed, so I imagine the next push of the site will resolve this and several other formatting issues.