edittemplate: use unambiguous RFC 3339 datestamps

These take into account the timezone offset (and convert it to UTC+0000)
rather than being in an unspecified timezone.

IkiWiki/Plugin/edittemplate.pm

@@ -156,7 +156,7 @@ sub filltemplate ($$) {
 	}
 
 	my $time = time();
-	$template->param(time => IkiWiki::formattime($time, "%Y-%m-%d %H:%M:%S"));
+	$template->param(time => IkiWiki::date_3339($time));
 
 	return $template->output;
 }

doc/ikiwiki/directive/edittemplate.mdwn

@@ -39,6 +39,8 @@ These variables might be set:
   (Requires the `UUID::Tiny` Perl module if not running on Linux.)
 
 * `<TMPL_VAR time>` is replaced with the current (template generation)
-  time, using a fixed format, `%Y-%m-%d %H:%M:%S`.
+  time using a fixed format (RFC 3339, `%Y-%m-%dT%H:%M:%SZ`),
+  suitable for use in `\[[!meta date="<TMPL_VAR time>"]]`
+  (see [[meta]]) or `\[[!date "<TMPL_VAR time>"]]` (see [[date]]).
 
 [[!meta robots="noindex, follow"]]