Publishes a Notion database with a date property to a calendar feed.

1. Create a Notion integration in http://notion.so/profile/integrations
2. Go to the Notion database -> click ••• from top right -> Connections -> Connect to, select the integration from last step
3. Fork this val
4. Set NOTION_API_TOKEN and NOTION_EVENTS_DATABASE_ID in https://www.val.town/settings/environment-variables
5. Update datePropertyName and maxEventAgeInMonths if necessary