Refactor redis keys and store messages in protobuf

Changes:
- Task messages are stored under "asynq:{<qname>}:t:<task_id>" key in redis, value is a HASH type and message are stored under "msg" key in the hash. The hash also stores "deadline", "timeout".
- Redis LIST and ZSET stores task message IDs
- Task messages are serialized using protocol buffer

inspeq/inspector_test.go

@@ -518,8 +518,8 @@ func TestInspectorListPendingTasks(t *testing.T) {
 	defer r.Close()
 	m1 := h.NewTaskMessage("task1", nil)
 	m2 := h.NewTaskMessage("task2", nil)
-	m3 := h.NewTaskMessage("task3", nil)
-	m4 := h.NewTaskMessage("task4", nil)
+	m3 := h.NewTaskMessageWithQueue("task3", nil, "critical")
+	m4 := h.NewTaskMessageWithQueue("task4", nil, "low")
 
 	inspector := New(getRedisConnOpt(t))
 
@@ -587,8 +587,8 @@ func TestInspectorListActiveTasks(t *testing.T) {
 	defer r.Close()
 	m1 := h.NewTaskMessage("task1", nil)
 	m2 := h.NewTaskMessage("task2", nil)
-	m3 := h.NewTaskMessage("task3", nil)
-	m4 := h.NewTaskMessage("task4", nil)
+	m3 := h.NewTaskMessageWithQueue("task3", nil, "custom")
+	m4 := h.NewTaskMessageWithQueue("task4", nil, "custom")
 
 	inspector := New(getRedisConnOpt(t))
 
@@ -1254,13 +1254,13 @@ func TestInspectorArchiveAllPendingTasks(t *testing.T) {
 		},
 		{
 			pending: map[string][]*base.TaskMessage{
-				"default": {m3, m4},
+				"default": {m3},
 			},
 			archived: map[string][]base.Z{
 				"default": {z1, z2},
 			},
 			qname: "default",
-			want:  2,
+			want:  1,
 			wantPending: map[string][]*base.TaskMessage{
 				"default": {},
 			},
@@ -1269,7 +1269,6 @@ func TestInspectorArchiveAllPendingTasks(t *testing.T) {
 					z1,
 					z2,
 					base.Z{Message: m3, Score: now.Unix()},
-					base.Z{Message: m4, Score: now.Unix()},
 				},
 			},
 		},