Flatbuffers library added to the list of third party libraries.

third_party/flatbuffers/conan/appveyor/build.py

@@ -0,0 +1,8 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+import os
+
+if os.getenv("APPVEYOR_REPO_TAG") != "true":
+    print("Skip build step. It's not TAG")
+else:
+    os.system("python conan/build.py")

third_party/flatbuffers/conan/appveyor/install.py

@@ -0,0 +1,8 @@
+#!/usr/bin/env python
+# -*- coding: utf-8 -*-
+import os
+
+if os.getenv("APPVEYOR_REPO_TAG") != "true":
+    print("Skip step. It's not TAG")
+else:
+    os.system("pip install conan conan-package-tools")