Add snippet generating ISO-formatted date

I am a big fan of the ISO date+time format, because it is our only hope
to overcome endless mess which are current zillion non-sensical national
formats.

snippets/_.snippets

@@ -7,6 +7,8 @@ snippet date
 	`strftime("%Y-%m-%d")`
 snippet ddate
 	`strftime("%B %d, %Y")`
+snippet diso
+	`strftime("%Y-%m-%dT%H:%M:%S")`
 snippet time
 	`strftime("%H:%M")`
 snippet datetime