Add skeleton hint router

The hint router will perform its scheduling solely based upon hints
provided by a filter (e.g. namedserverfilter) placed before it.

server/modules/routing/hintrouter/hintroutersession.hh

@@ -0,0 +1,45 @@
+#pragma once
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2019-07-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include <maxscale/cppdefs.hh>
+#include <maxscale/router.hh>
+
+class HintRouter;
+
+class HintRouterSession : public maxscale::RouterSession
+{
+public:
+    HintRouterSession(MXS_SESSION* pSession,
+                      HintRouter*  pRouter);
+
+    ~HintRouterSession();
+
+    void close();
+
+    int32_t routeQuery(GWBUF* pPacket);
+
+    void clientReply(GWBUF* pPacket, DCB* pBackend);
+
+    void handleError(GWBUF*             pMessage,
+                     DCB*               pProblem,
+                     mxs_error_action_t action,
+                     bool*              pSuccess);
+
+private:
+    HintRouterSession(const HintRouterSession&);
+    HintRouterSession& operator = (const HintRouterSession&);
+
+private:
+    HintRouter* m_pRouter;
+};