Make RdKafka.Offset fields const
Make RdKafka.Offset fields const

https://github.com/ah-/rdkafka-dotnet/issues/39
MrGlenThomas/confluent-kafka-dotnet,treziac/confluent-kafka-dotnet,bjornicus/confluent-kafka-dotnet,bjornicus/confluent-kafka-dotnet,treziac/confluent-kafka-dotnet,ah-/rdkafka-dotnet,MrGlenThomas/confluent-kafka-dotnet,MaximGurschi/rdkafka-dotnet