added support for formatted datetimes

fgs/datatypes.py

@@ -362,6 +362,10 @@ class Date:
     def isoformat(self):
         return self.dt.isoformat()
 
+    def strftime(self, formatstr):
+        # https://docs.python.org/3/library/datetime.html#strftime-and-strptime-format-codes
+        return self.dt.strftime(formatstr)
+
     def __lt__(self, other):
         return self.dt.timestamp() < other.dt.timestamp()