Implemented PhpAmqpLibHandler

I've implemented an handler (and tests) for AMQP using php-amqplib.

I know that there is already an AMQP handler but it requires the php extension, which may not be present. Also, for symfony project php-amqplib may be the only (quick) way for using AMPQ, since there is already a well-done bundle for symfony (https://github.com/videlalvaro/rabbitmqbundle).

I've based my implementation from `AmqpHandler.php`, but a common abstract class seem overkill to me.