memory growth fix

source of memory growth has been found on clear function, which probably doesn't actually delete memory, instead of leaving it for futue usage.

this change introduces function deep_clean which actually deletes collection and returns same type (of given collection to clear)

related to: #151 (closed) source: https://chase-seibert.github.io/blog/2013/08/03/diagnosing-memory-leaks-python.html