Review and fix issues with find

[shcheklein]

          okay, problems that I see:

• maxdepth is not supported
• withdirs is not supported (must have for expand path)
• doesn't check bucket name find('.') and find('etasderwer') return the same result
• it keeps appending ids to cache every time even for already known
• cache is not locked (multithreading support) - this is a bit more advanced and less critical to start with

Originally posted by @shcheklein in #229 (comment)