Node Event Storage Versions Save

This release is a breaking change, since the file format of partitions was changed.

• Consumers can store state with exactly-once semantics
• Node 6 no longer supported
• dependency version updates

Fix tests

Add missing index entry point

• Consumers may start from an arbitrary revision

• JoinEventStream returns cross-stream events deterministically (this makes commitId a counter instead of uuid and hence is breaking)
• object stream matcher is persisted correctly
• Consumer pauses the underlying stream on stop
• Storage can lazy load indexes
• rename privateKey storage option to hmacSecret
• add Readme sections on compression and security

• Fix and cover JoinEventStream with tests
• Improve Index.find and cover Index with more tests
• Some small code improvements

• Add hmac verification for Index matcher
• Improve Index read API to read from the end
• Allow disabling dirty reads