Tidy up core sources:

The core headers are moved to their own directory (but remain in
the same namespace).

test/core/detail/base64.cpp

@@ -0,0 +1,44 @@
+//
+// Copyright (c) 2013-2016 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)
+//
+
+// Test that header file is self-contained.
+#include <beast/core/detail/base64.hpp>
+
+#include <beast/unit_test/suite.hpp>
+
+namespace beast {
+namespace detail {
+
+class base64_test : public beast::unit_test::suite
+{
+public:
+    void
+    check (std::string const& in, std::string const& out)
+    {
+        auto const encoded = base64_encode (in);
+        expect (encoded == out);
+        expect (base64_decode (encoded) == in);
+    }
+
+    void
+    run()
+    {
+        check ("",       "");
+        check ("f",      "Zg==");
+        check ("fo",     "Zm8=");
+        check ("foo",    "Zm9v");
+        check ("foob",   "Zm9vYg==");
+        check ("fooba",  "Zm9vYmE=");
+        check ("foobar", "Zm9vYmFy");
+    }
+};
+
+BEAST_DEFINE_TESTSUITE(base64,core,beast);
+
+} // detail
+} // beast
+