This patch contains three how-to related to datetime:

1)How to convert a datetime column to string and back again to datetime
2)How to convert a datetime column to unix timestamp
3)How to split datetime column into multiple column
datetime how-to
Update convert_column_to_timestamp.py
Update convert_column_to_timestamp.py
Update split_datetime_column.py
Update README.md
Merge pull request #9 from graphlab-code/datetime-how-to

This patch contains three how-to related to datetime: