add method
Add a some value to current date,
Implementation
EDateTime add({
int year = 0,
int month = 0,
int day = 0,
int hour = 0,
int minute = 0,
int second = 0,
int millisecond = 0,
int microsecond = 0,
}) {
_date = DateTime(
_date.year + year,
_date.month + month,
_date.day + day,
_date.hour + hour,
_date.minute + minute,
_date.second + second,
_date.millisecond + millisecond,
_date.microsecond + microsecond);
return EDateTime.fromDateTime(_date);
}