Function std.datetime.systime.SysTime.toISOExtString
Converts this SysTime to a string with the format
        YYYY-MM-DDTHH:MM:SS.FFFFFFFTZ (where F is fractional seconds and TZ
        is the time zone).
						
				string toISOExtString() nothrow scope @safe const;
				
				
				void toISOExtString(W)
				(
				
				  ref W writer
				
				) const scope
				
				if (isOutputRange!(W, char));
						
					
				Note that the number of digits in the fractional seconds varies with the number of fractional seconds. It's a maximum of 7 (which would be hnsecs), but only has as many as are necessary to hold the correct value (so no trailing zeroes), and if there are no fractional seconds, then there is no decimal point.
        If this SysTime's time zone is
        LocalTime, then TZ is empty. If its time
        zone is UTC, then it is "Z". Otherwise, it is the offset from UTC
        (e.g. +01:00 or -07:00). Note that the offset from UTC is not
        enough to uniquely identify the time zone.
Time zone offsets will be in the form +HH:MM or -HH:MM.
Parameters
| Name | Description | 
|---|---|
| writer | A characcepting
            output range | 
Returns
A string when not using an output range; void otherwise.
Example
import core