Convert OpenRC to a centralized copyright/license structure

In the past, OpenRC was a hybrid of a centralized and file-scope
license/copyright structure.

I followed the instructions from the Software Freedom Law Center [1] to
convert to a Centralized structure where possible, for easier future
maintenance.

[1] https://softwarefreedom.org/resources/2012/ManagingCopyrightInformation.html

Makefile

@@ -1,6 +1,12 @@
-# OpenRC Makefile
-# Copyright (c) 2007-2009 Roy Marples <roy@marples.name>
-# Released under the 2-clause BSD license.
+# Copyright (c) 2007-2015 The OpenRC Authors.
+# See the Authors file at the top-level directory of this distribution and
+# https://github.com/OpenRC/openrc/blob/master/AUTHORS
+#
+# This file is part of OpenRC. It is subject to the license terms in
+# the LICENSE file found in the top-level directory of this
+# distribution and at https://github.com/OpenRC/openrc/blob/master/LICENSE
+# This file may not be copied, modified, propagated, or distributed
+# except according to the terms contained in the LICENSE file.
 
 TOP:=		${dir ${realpath ${firstword ${MAKEFILE_LIST}}}}
 MK=			${TOP}/mk