* Support CSV file in DMatrix
We'd just need to expose the CSV parser in dmlc-core to the Python wrapper
* Revert extra code; document existing CSV support
CSV support is already there but undocumented
* Add notice about categorical features
* Fix doc build
ReadTheDocs build has been broken for a while due to incompatibilities between
commonmark, recommonmark, and sphinx. See:
* "Recommonmark not working with Sphinx 1.6"
https://github.com/rtfd/recommonmark/issues/73
* "CommonMark 0.6.0 breaks compatibility"
https://github.com/rtfd/recommonmark/issues/24
For now, we fix the versions to get the build working again
* Fix search bar
