added gpl license file

code/license

+/* Copyright (C) 2021  Hubert Berezowski */
+
+/* This program is free software: you can redistribute it and/or modify */
+/* it under the terms of the GNU General Public License as published by */
+/* the Free Software Foundation, either version 3 of the License, or */
+/* (at your option) any later version. */
+
+/* This program is distributed in the hope that it will be useful, */
+/* but WITHOUT ANY WARRANTY; without even the implied warranty of */
+/* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the */
+/* GNU General Public License for more details. */
+
+/* You should have received a copy of the GNU General Public License */
+/* along with this program.  If not, see <https://www.gnu.org/licenses/>. */
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