Declutter root dir: COPYRIGHT --> COPYING

No need to keep a COPYING (GPL v2 license) AND a file COPYRIGHT in
the root. All files have the boilerplate anyway. Add the relevant
part on top of the COPYING file and do away with COPYRIGHT.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

COPYING

@@ -1,3 +1,13 @@
+# 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 2 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.
+
                     GNU GENERAL PUBLIC LICENSE
                        Version 2, June 1991