- proto3 support
- backward compatible with proto2
does not compile with gcc 5.4:
In file included from google/protobuf/stubs/mathlimits.cc:36:0:
./google/protobuf/stubs/mathlimits.h:203:315: error: overflow in constant expression [-fpermissive]
./google/protobuf/stubs/mathlimits.h:203:315: error: overflow in constant expression [-fpermissive]
./google/protobuf/stubs/mathlimits.h:203:315: error: overflow in constant expression [-fpermissive]