add method to get ngraph version string (#1966)

src/ngraph/CMakeLists.txt

@@ -34,6 +34,7 @@ set (SRC
     file_util.cpp
     function.cpp
     log.cpp
+    ngraph.cpp
     node.cpp
     op/abs.cpp
     op/acos.cpp

src/ngraph/ngraph.cpp

+//*****************************************************************************
+// Copyright 2017-2018 Intel Corporation
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//*****************************************************************************
+
+extern "C" const char* get_ngraph_version_string()
+{
+    return NGRAPH_VERSION;
+}