Add ssl_stream to experimental:

The ssl_stream wrapper provides C++11 move semantics for ssl::stream,
as well as incorporating the flat_stream workaround for a performance
problem with ssl::stream writes and buffer sequences having length
greater than one.

test/beast/experimental/ssl_stream.cpp

@@ -0,0 +1,15 @@
+//
+// 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
+//
+
+#if BOOST_BEAST_USE_OPENSSL
+
+// Test that header file is self-contained.
+#include <boost/beast/experimental/core/ssl_stream.hpp>
+
+#endif