Refactored to utilize `php-amqp` extension for AMQP

This will remove the requirement for pure php library for AMQP
connectivity and connection managment.
Merge branch 'master' into enhancement/refactor-to-ext-amqp

Conflicts:
	composer.json
Merge remote-tracking branch 'origin/enhancement/refactor-to-ext-amqp' into enhancement/refactor-to-ext-amqp

Conflicts:
	.travis.yml
	composer.json
	library/Rhubarb/Broker/AbstractBroker.php
	library/Rhubarb/Broker/Amqp.php
	library/Rhubarb/ResultStore/Amqp.php
	tests/library/Rhubarb/RhubarbTest.php