Add licence header

include/duckhandy/resource_pool.hpp

@@ -1,4 +1,22 @@
-#pragma once
+/* Copyright 2016-2018 Michele Santullo
+ * This file is part of "duckhandy".
+ *
+ * "duckhandy" 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.
+ *
+ * "duckhandy" 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 "duckhandy".  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#ifndef id932FF9EFA6DC4EE1A0914178319B0388
+#define id932FF9EFA6DC4EE1A0914178319B0388
 
 #include <set>
 #include <utility>
@@ -115,3 +133,5 @@ namespace dhandy {
 		}
 	}
 } //namespace dhandy
+
+#endif