Persistence formatting about jsonpydexer HOT 4 OPEN

{
    "files": { // all the files in the index
        "filenameA.json": "1500000000", // the last time we touched this file's entry[s] in the index
        "somedirectory/filenameB.json": "1500000200",
        "filenameC.json": "1500000500"
    }, 
    "unique_indices": { // keynames which no two files have duplicate values for
        "(id,)": { // keynames are serialized as tuples surrounded by parens, with a trailing comma if the key is non-nested
            "foo_001": "filenameA.json", // keyvalue:filename pair
            "foo_002": "somedirectory/filenameB.json",
            "foo_005:" "filenameC.json",
        },
        // ... more keynames go here
    "group_indices": { // keynames which two or more files have a duplicate value for
        "(name, first)": { // an example of a nested key's keyname
            "alice": [ // group_indices keyvalue:filename pairs are always string:list[string]
                "filenameA.json",
                "filenameC.json"
            ],
            "bob": [
                "somedirectory/filenameB.json"
            ]
        }
    }
}