Applications consuming our library wants generally to declare the broker
in the configuration, including its type.
We provide a BrokerFactory::make method to instanciate a broker with
an array like this:
[ "driver" => "amqp", "host" => "rabbit.domain.tld", "port" => "5672", "username" => "lorem", "password" => "ipsum", "vhost" => "dolor", ]
The file drivers.php contains the map between the drivers names
and the classses to load.
Each broker class implements a makeFromConfig ($params) static method
to build an object from such array.
The BrokerFactory::make method gets from drivers.php the correct class,
then calls makeFromConfig and returns the result.