First pre-release after rewrite to use v2 protobuf API

added benchmark for the receiveQueue

To run this benchmark:
go test -bench=BenchmarkReceiveQueue

Results on my machine are pretty conclusive:
BenchmarkReceiveQueue/RWMutexMap-12                 13286848                77.7 ns/op
BenchmarkReceiveQueue/syncMapStruct-12               2467936               482 ns/op
BenchmarkReceiveQueue/syncMapDirect-12               2494368               485 ns/op