add flush and reopen methods to the logger

vlib/log/log.v

@@ -80,6 +80,16 @@ pub fn (mut l Log) close() {
 	l.ofile.close()
 }
 
+// reopen reopens the log file.  Useful for log rotation.
+// This does nothing if you are only writing to the console.
+pub fn (mut l Log) reopen() {
+	if l.output_target == .file || l.output_target == .both {
+		l.ofile.reopen(l.output_file_name, 'ab') or {
+			panic('error while re-opening log file ${l.output_file_name} for appending')
+		}
+	}
+}
+
 // log_file writes log line `s` with `level` to the log file.
 fn (mut l Log) log_file(s string, level Level) {
 	timestamp := time.now().format_ss_micro()

vlib/log/logger_interface.v

@@ -11,5 +11,7 @@ mut:
 	debug(s string)
 	// utility methods:
 	set_level(level Level)
+	flush()
+	reopen()
 	free()
 }