Allow jobs to be manually failed

Laravel Jobs can be manually failed with $job->fail() with an optional \Throwable - this release provides the transport capabilities for the response to handle this use case and the corresponding tests.

Resolve exception handling issues

Previously exception handling worked by passing a serialized Throwable across the transport, however there are some edge cases that cause the Exception to corrupt due to the nature of that serialization.

In favour of stability, I've pulled that functionality in favour of pulling the exception values from the exception object (losing the stack context, but retaining the stack as a string). Which is far more robust.

Resolves minor bug

This release resolves a minor bug with the response data not being broken out of it's underlying array.

Initial Release

Initial release.