Add propert license information

COPYING

@@ -0,0 +1,20 @@
+VAT identification number extension for PostgreSQL
+
+Copyright (c) 2023 jordi fita mas <jordi@tandem.blog>
+
+Permission to use, copy, modify, and distribute this software and its
+documentation for any purpose, without fee, and without a written
+agreement is hereby granted, provided that the above copyright notice
+and this paragraph and the following two paragraphs appear in all
+copies.
+
+IN NO EVENT SHALL JORDI FITA MAS BE LIABLE TO ANY PARTY FOR DIRECT,
+INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES, INCLUDING LOST
+PROFITS, ARISING OUT OF THE USE OF THIS SOFTWARE AND ITS DOCUMENTATION,
+EVEN IF DATAHOUSE AG HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+
+JORDI FITA MAS SPECIFICALLY DISCLAIMS ANY WARRANTIES, INCLUDING, BUT
+NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
+FOR A PARTICULAR PURPOSE. THE SOFTWARE PROVIDED HEREUNDER IS ON AN
+"AS IS" BASIS, AND DATAHOUSE AG HAS NO OBLIGATIONS TO PROVIDE
+MAINTENANCE, SUPPORT, UPDATES, ENHANCEMENTS, OR MODIFICATIONS.

es.c

@@ -1,7 +1,7 @@
 /*
  * SPDX-FileCopyrightText: 2023 jordi fita mas <jfita@peritasoft.com>
  *
- * SPDX-License-Identifier: GPL-3.0-only
+ * SPDX-License-Identifier: PostgreSQL
  */
 #include "es.h"
 #include <stdbool.h>

es.h

@@ -1,7 +1,7 @@
 /*
  * SPDX-FileCopyrightText: 2023 jordi fita mas <jfita@peritasoft.com>
  *
- * SPDX-License-Identifier: GPL-3.0-only
+ * SPDX-License-Identifier: PostgreSQL
  */
 #ifndef VAT_ES_H
 #define VAT_ES_H 1

vat--0.0.sql

@@ -1,4 +1,8 @@
-/* vatin--0.0.sql */
+/*
+ * SPDX-FileCopyrightText: 2023 jordi fita mas <jfita@peritasoft.com>
+ *
+ * SPDX-License-Identifier: PostgreSQL
+ */
 
 -- complain if script is sources in psql, rather than via CREATE EXTENSION
 \echo Use "CREATE EXTENSION vat" to load this file. \quit

vatin.c

@@ -1,7 +1,7 @@
 /*
  * SPDX-FileCopyrightText: 2023 jordi fita mas <jfita@peritasoft.com>
  *
- * SPDX-License-Identifier: GPL-3.0-only
+ * SPDX-License-Identifier: PostgreSQL
  */
 
 #include <postgres.h>