Cldr Dates Times vision 2.1.0

Enhancements

• All calling Date, Time and DateTime to_string/3 as to_string/1 omitting the backend and providing options. The backend will default to Cldr.default_backend(). An exception will be raised if there is no default backend.

• Updates to ex_cldr_calendars 1.0 which includes Cldr.Calendar.week_of_month/1. The result corresponds to the W format which is now implemented as well.