deque is much better fitted than a simple Python list
Indeed, a standard Python list is stored as an array, and has to be reallocated
all the time, while a deque has very fast operation on both ends, and the fixed
size mode will automatically drop first element when pushing to a full deque.
Also it was crazy to store the whole log. Storing 10000 log lines seems decent
and shouldn't take way too much space (less than 512KB based on a quick
estimation).
This might fix #292 and #353.