Syntax:
KEY[>=,<=,>,<,=,:]VALUE VALUE is expected to be json dump except when the delimiter is ":" With ":" delimiter, accepted special words are "maximum", "max", "latest" and "minimum", "min" and "oldest".
Selection:
For the sake of lisibility, the shadir entries are preprocessed in order to eliminate invalid metadata. This is slower but the metadata is exepected to be small as each entry may require a database access on the server shacache side.
JSON file:
Support metadata in json file.