Use ISO-8601 format for toString call on Date and DateTime

Papaparse call toString to write values. So to ensure the same format between
clients, toString on Date and DateTime must return ISO-8601 format with space
as time separator.

issue7305
review36161002

src/sao.js

@@ -121,6 +121,9 @@ var Sao = {};
         date.date(day);
         date.set({hour: 0, minute: 0, second: 0, millisecond: 0});
         date.isDate = true;
+        date.toString = function() {
+            return this.format('YYYY-MM-DD');
+        };
         return date;
     };
 
@@ -166,6 +169,13 @@ var Sao = {};
             datetime.milliseconds(millisecond);
         }
         datetime.isDateTime = true;
+        datetime.toString = function() {
+            if (this.milliseconds()) {
+                return this.format('YYYY-MM-DD HH:mm:ss.SSSSSS');
+            } else {
+                return this.format('YYYY-MM-DD HH:mm:ss');
+            }
+        };
         datetime.local();
         return datetime;
     };