Better date time support

[KallynGowdy]

• Added the ability to store dates in tags by prefixing them with 📅.
  • Dates must be formatted similarly to ISO 8601:
    • 2012-02-06 (year-month-day in UTC-0 time zone)
    • 2015-08-16T08:45:00 (year-month-day + hour:minute:second in UTC-0 time zone)
    • 2015-08-16T08:45:00 America/New_York (year-month-day + hour:minute:second in specified time zone)
    • 2015-08-16T08:45:00 local (year-month-day + hour:minute:second + in local time zone)
  • In scripts, date tags are automatically parsed and converted to DateTime objects.
    • DateTime objects are easy-to-use representations of date and time with respect to a specific time zone.
    • They work better than the built-in Date class because DateTime supports time zones whereas Date does not.
    • You can learn more about them by checking out the documentation.
• Added the getDateTime(value) function to make parsing strings into DateTime objects easy.
  • Parses the given value and returns a new DateTime that represents the date that was contained in the value.
  • Returns null if the value could not be parsed.