Memory limit and dynamic and non hard-coded content-type and delivery-mode

Good afternoon,

I'm pulling request you some changes I've developed on this bundle to my project.

   - I've added a new option to the consumer command in order to establish a memory limit  to  the consumer process. 

   - I've added two setters in Producer service in order to allow developer to set a value for content-type and delivery-mode. Default values are still 'text/plain' and 2

Regards

Nacho