Add and parse cpp_friend

Only works in clang>=4.

src/cpp_friend.cpp

@@ -0,0 +1,26 @@
+// Copyright (C) 2017 Jonathan Müller <jonathanmueller.dev@gmail.com>
+// This file is subject to the license terms in the LICENSE file
+// found in the top-level directory of this distribution.
+
+#include <cppast/cpp_friend.hpp>
+
+#include <cppast/cpp_entity_kind.hpp>
+
+using namespace cppast;
+
+cpp_entity_kind cpp_friend::kind() noexcept
+{
+    return cpp_entity_kind::friend_t;
+}
+
+cpp_entity_kind cpp_friend::do_get_entity_kind() const noexcept
+{
+    return kind();
+}
+
+bool cppast::is_friended(const cpp_entity& e) noexcept
+{
+    if (is_templated(e))
+        return is_friended(e.parent().value());
+    return e.parent() && e.parent().value().kind() == cpp_entity_kind::friend_t;
+}