* fix merge issues of DataEnvelope and its pruning
* simplify by removing the tombstones, which didn't work in all cases anyway
* keep the PruningPerformed markers in the DataEnvelope until configured
TTL has elapsed (wall clock)
* simplify PruningState structure
* also store the pruning markers in durable data
* collect removed nodes from the data, listing on MemberRemoved is not enough
* possibility to disable pruning altogether
* documented caveat for durable data
- All Map types are now generic in their key: ORMap, ORMultiMap, LWWMap,
PNCounterMap
- test for binary compatibility with previous version for serialization
- entries are sorted for deterministic SHA-1 on same value
