Support for Mongo 3.6

MemoryBackend currently is coded to emulate Mongo 3.0.0 - any plans on supporting newer versions (3.6.0)? 

This would require updating the OpCode handling as 3.6 introduces a new OpCode that is not currently supported (#2013)
https://github.com/bwaldvogel/mongo-java-server/blob/7449324635c686aa631faa35a08d18c030b03c3d/core/src/main/java/de/bwaldvogel/mongo/wire/OpCode.java#L16