1.3
  - Fix for CRAN: do not use CXXCPP

1.2
  - Windows: update to protobuf 3.8.0 with support for GCC 8+
  - Suppress warnings about pragmas in autogenerated protobuf headers

1.1
  - Windows: update to protobuf 3.5.1 (to support gcc 8.1.0 toolchain)
