* Aristo+RocksDB: Update backend drivers
why:
RocksDB update allows use some of the newly provided methods which
were previously implemented by using the very C backend (for the lack
of NIM methods.)
* Aristo+RocksDB: Simplify drivers wrapper
* Kvt: Update backend drivers and wrappers similar to `Aristo`
* Aristo+Kvm: Use column families for RocksDB
* Aristo+MemoryDB: Code cosmetics
* Aristo: Provide guest column family for export
why:
So `Kvt` can piggyback on `Aristo` so there avoiding to run a second
DBMS system in parallel.
* Kvt: Provide import mechanism for RoksDB guest column family
why:
So `Kvt` can piggyback on `Aristo` so there avoiding to run a second
DBMS system in parallel.
* CoreDb+Aristo: Run persistent `Kvt` DB piggybacked on `Aristo`
why:
Avoiding to run two DBMS systems in parallel.
* Fix copyright year
* Ditto
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