Use a fixed-size deque for storing the log

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.

printcore.py

@@ -20,6 +20,7 @@ from threading import Thread
 from select import error as SelectError
 import time, getopt, sys
 import platform, os
+from collections import deque
 from GCodeAnalyzer import GCodeAnalyzer
 
 def control_ttyhup(port, disable_hup):
@@ -54,7 +55,7 @@ class printcore():
         self.resendfrom = -1
         self.paused = False
         self.sentlines = {}
-        self.log = []
+        self.log = deque(maxlen = 10000)
         self.sent = []
         self.tempcb = None #impl (wholeline)
         self.recvcb = None #impl (wholeline)
@@ -342,7 +343,7 @@ class printcore():
         while self.printing and self.printer and self.online:
             self._sendnext()
         self.sentlines = {}
-        self.log = []
+        self.log.clear()
         self.sent = []
         try:
           self.print_thread.join()