Add teardown_role for correct TIME_WAIT behavior (API Change):

* teardown_tag is replaced with teardown_role, a client/server
  flag used to determine whether the shutdown is performed
  before or after reading the EOF. This is in accordance with
  RFC6455 7.1.1:

  https://tools.ietf.org/html/rfc6455#section-7.1.1

Actions Required:

* Modify signatures of teardown and async_teardown to use
  teardown_role instead of teardown_tag

* Change calls to teardown and async_teardown to pass the
  correct role: client or server depending on context.

test/beast/websocket/role.cpp

@@ -0,0 +1,11 @@
+//
+// Copyright (c) 2016-2017 Vinnie Falco (vinnie dot falco at gmail dot com)
+//
+// Distributed under the Boost Software License, Version 1.0. (See accompanying
+// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
+//
+// Official repository: https://github.com/boostorg/beast
+//
+
+// Test that header file is self-contained.
+#include <boost/beast/websocket/role.hpp>