Replication objects and sub-binaries

[martinsumner]

Buckets and Keys are pattern matched in nextgenrepl replication binaries - so that they be treated within the memory management as sub-binaries. A reference will be kept for the Bucket/Key - potentially until the Bucket/Key is persisted to a L0 file - but this means that a reference to the replicated binary must be kept.

It would be more efficient to binary:copy/1 the Type/Bucket/Key when extracting so that the full replication object can be de-referenced once it has been decoded.