replace keys.csv with persistent map

block-storage/src/main/java/org/lucares/pdb/map/PersistentMap.java

@@ -190,7 +190,7 @@ public class PersistentMap<K, V> implements AutoCloseable {
 
     /**
      * 
-     * @param path            file relative to {@code storageBasePath}
+     * @param path            file for the index, must be child of storageBasePath
      * @param storageBasePath base path
      * @param keyEncoder      encoder for keys
      * @param valueEncoder    encoder for values