Use timers not affected by system clock updates (#42)

See paragraph two of https://docs.python.org/3/library/time.html#time.time

kademlia/routing.py

@@ -16,7 +16,7 @@ class KBucket(object):
         self.ksize = ksize
 
     def touchLastUpdated(self):
-        self.lastUpdated = time.time()
+        self.lastUpdated = time.monotonic()
 
     def getNodes(self):
         return list(self.nodes.values())
@@ -136,7 +136,7 @@ class RoutingTable(object):
         Get all of the buckets that haven't been updated in over
         an hour.
         """
-        hrago = time.time() - 3600
+        hrago = time.monotonic() - 3600
         return [b for b in self.buckets if b.lastUpdated < hrago]
 
     def removeContact(self, node):

kademlia/storage.py

@@ -52,7 +52,7 @@ class ForgetfulStorage(IStorage):
     def __setitem__(self, key, value):
         if key in self.data:
             del self.data[key]
-        self.data[key] = (time.time(), value)
+        self.data[key] = (time.monotonic(), value)
         self.cull()
 
     def cull(self):
@@ -78,7 +78,7 @@ class ForgetfulStorage(IStorage):
         return repr(self.data)
 
     def iteritemsOlderThan(self, secondsOld):
-        minBirthday = time.time() - secondsOld
+        minBirthday = time.monotonic() - secondsOld
         zipped = self._tripleIterable()
         matches = takewhile(lambda r: minBirthday >= r[1], zipped)
         return list(map(operator.itemgetter(0, 2), matches))