Adds reminder functionality for collection.NotionDate

[jefftangx]

This allows reminders to be set programmatically. Demo

[jamalex]

Thanks for the PR, and sorry for the slow response!

Looks like this would also be covered by #49 -- do you (or others) have a strong preference of the class-based vs raw-dict-based approach for this? The library has tended to favor class-based, but this does look to be a simple enough data structure that it may be overkill.

[offlinehacker]

Thanks, works for me, using like:

row.date = NotionDate(start=today + datetime.timedelta(days=1), reminder={'time': "9:00", 'unit': "day", 'value': 0})

[KShivendu]

Can you please provide another example for its usage ? The one mentioned here didn't work for me.

[jamalex]

Thanks! Has now been merged in via #239, along with some additional fixes.