bin search on db file with only one entry fix; added flush and purge commands to ConsoleListener — flush force to drop db to file, purge recommend to collect garbage
FR5: check for fast creating merge and other files (during merge of 2 very small files can pass less than 1ms and name collusion — wait 5 ms to fix)  and 2 stress-tests to garbage collector (test with 100000keys and flush every 500 keys, garbage start working if in db dir more than 8 files,  test 1M keys, 1k values, default dump (≈100M), ≈10 files, garbage collector start with > 2 files in dir)