adds pluggable brokers

* added redis broker
 * added django_redis broker
 * added task acknowledgement

django_q/brokers/__init__.py

@@ -0,0 +1,47 @@
+from django_q.conf import Conf
+
+
+class Broker(object):
+    def __init__(self, list_key=Conf.Q_LIST):
+        self.connection = self.get_connection()
+        self.list_key = list_key
+
+    def enqueue(self, task):
+        pass
+
+    def dequeue(self):
+        pass
+
+    def queue_size(self):
+        pass
+
+    def delete_queue(self, list_key=None):
+        pass
+
+    def acknowledge(self, ack_id):
+        pass
+
+    def ping(self):
+        pass
+
+    def set(self, key, value, timeout):
+        pass
+
+    def get(self, key):
+        pass
+
+    def get_pattern(self, pattern):
+        pass
+
+    @staticmethod
+    def get_connection():
+        return 0
+
+
+def get_broker(list_key=Conf.Q_LIST):
+    if Conf.REDIS:
+        from brokers import redis
+        return redis.Redis(list_key=list_key)
+    elif Conf.DJANGO_REDIS:
+        from brokers import django_redis
+        return django_redis.DjangoRedis(list_key=list_key)