Fix #293 , Refactor tweet_annual_days

[JasirZaeem]

Refactored tweet_annual_days to make the following changes:

• Stop repetition of events with relative dates.
• Added ability to have multiple events on the same day.
• Fixed and improved how events are chosen from the list of all events.

[VickiLanger]

Thanks for all the fixes! I love that we now have the ability to have multiple events on one day and it chooses one at random.