Memory leaks in the Python backend

Although most memory leaks have been mitigated with the release 0.1.3 of this package (optimization of struct.pack into numpy.tostring/numpy.tobytes), there seems still to exist a very mild memory leak. It is visible when one executes processes that access large amounts of data (such as in the Replay Attack dataset).

This problems needs to be investigated in a more closed setting for a leak-free execution.