adding stop functionality for graceful shutdown

[odedva]

• adding an internal variable _should_listen for managing the state of the endless for loop
  • this variable also will stop the messages loop in case there are many messages received in the batch
• exposing a stop function to stop listening and making the listen function to return

[odedva]

hey - @jegesh would you be able to take a look on this ?

[jegesh]

Hi! Thanks for the contribution. I'm just not clear on the use case you're addressing in this PR. Please explain

[odedva]

hey - if this is running in a thread, it would be nice to be able to gracefully shutdown the consumption of messages so the application that manages this thread with listener can ext nicely