obshashrange: "update" the cache on each transaction close Right now the "update" does not really file the cache, but it will detect invalid situation and clean them.

obshashrange: properly invalidate the cache on destroyed Copy paste is the scurge of code source.

obshashrange: properly drop the current connection on clear

obshashrange: exit early if nothing to write

obshashrange: use the dualsourcecache as a base for the cache This will easily open the way to incrementally updated obshashrange cache. Small update are needed to the data base schema so be bump the version Currently the update function is not warming the cache (but details case where it is invalidated).

obscache: makes dualsourcecache compatible with obshashrange cache needs The goal of the abstract method is to be reusable. So we make sure it is reusable.

readme: add a changelog entry about the more efficient obscache