Add version info for public Python SQL API.
cc rxin
Author: Davies Liu <davies@databricks.com>
Closes#6295 from davies/versions and squashes the following commits:
cfd91e6 [Davies Liu] add more version for DataFrame API
600834d [Davies Liu] add version to SQL API docs
(cherry picked from commit 8ddcb25b39)
Signed-off-by: Reynold Xin <rxin@databricks.com>
dataframe.py is splited into column.py, group.py and dataframe.py:
```
360 column.py
1223 dataframe.py
183 group.py
```
Author: Davies Liu <davies@databricks.com>
Closes#6201 from davies/split_df and squashes the following commits:
fc8f5ab [Davies Liu] split dataframe.py into multiple files
(cherry picked from commit d7b69946cb)
Signed-off-by: Reynold Xin <rxin@databricks.com>
