Add HyperLogLog to the engine core #85
Description
HyperLogLog could be added to the engine core, so the user know approx. cardinality of the keys in the system.
This could also be a way for the system to track the cardinality of the records vs num of records, meaning we could make a new sort of compactions. Roughly we would have a certain percentage of the data be duplicated in the system, triggering the compactions. These are rough ideas for now, but could be added to the project.