+ * {@link QueueKeeper} implementation focused to keep order and use up mutiple threads for translation phase.
+ * <br/>
+ * There is internal thread pool of limited size ({@link QueueKeeperLightImpl#setPoolSize(int)})
+ * dedicated to translation. Then there is singleThreadPool dedicated to publishing (via popListeners)
+ * <br/>
+ * Workflow:
+ * <ol>
+ * <li>upon message push ticket is created and enqueued</li>
+ * <li>available threads from internal pool translate the massage wrapped in ticket</li>
+ * <li>when translation of particular message is finished, result is set in future result of wrapping ticket</br>
+ * (order of tickets in queue is not touched during translate)
+ * </li>
+ * <li>at the end of queue there is {@link TicketFinisher} running in singleThreadPool and for each ticket it does:
+ * <ol>
+ * <li>invoke blocking {@link BlockingQueue#take()} method in order to get the oldest ticket</li>
+ * <li>invoke blocking {@link Future#get()} on the dequeued ticket</li>
+ * <li>as soon as the result of translation is available, appropriate popListener is invoked</li>
+ * </ol>
+ * and this way the order of messages is preserved and also multiple threads are used by translating
+ * </li>
+ * </ol>
+ *
+ *