Major Description
There are some more commits remaining after the main codes were ported.
- https://github.com/databricks/koalas/commit/c8f803d6becb3accd767afdb3774c8656d0d0b47
- https://github.com/databricks/koalas/commit/913d68868d38ee7158c640aceb837484f417267e
