Generalized POST data generation.
Generalized Request generation.
Refactored SubscriberClient and added unsubscription support.
Added new test for subscriber client.
Fixed test output.
Merge branch 'feature/unsubscribe' into develop
Merge branch 'develop' into feature/manage-subscription-maintenance

Conflicts:
	src/SubscriberClient.php
	tests/phpunit/SubscriberClientTest.php
Fixed tests after merge.