add license information & rename typedefs

src/fen.h

@@ -1,8 +1,21 @@
+/* fen.h - fen notation.
+ *
+ * Copyright (C) 2021 Bruno Raoult ("br")
+ * Licensed under the GNU General Public License v3.0 or later.
+ * Some rights reserved. See COPYING.
+ *
+ * You should have received a copy of the GNU General Public License along with this
+ * program. If not, see <https://www.gnu.org/licenses/gpl-3.0-standalone.htmlL>.
+ *
+ * SPDX-License-Identifier: GPL-3.0-or-later <https://spdx.org/licenses/GPL-3.0-or-later.html>
+ *
+ */
+
 #ifndef FEN_H
 #define FEN_H
 
 #include "position.h"
 
-POS *fen2pos(POS *pos, char *fen);
+pos_t *fen2pos(pos_t *pos, char *fen);
 
 #endif