Add nanopb tool

rpc/tool/protoc-gen-nanopb

@@ -0,0 +1,11 @@
+#!/usr/bin/env python3
+# This file is used to invoke nanopb_generator.py as a plugin
+# to protoc on Linux and other *nix-style systems.
+# Use it like this:
+# protoc --plugin=protoc-gen-nanopb=..../protoc-gen-nanopb --nanopb_out=dir foo.proto
+
+from nanopb_generator import *
+
+if __name__ == '__main__':
+    # Assume we are running as a plugin under protoc.
+    main_plugin()