Instead of reporting just an error, jobs now respond with an object.
That object contains the return value from the job, or it's error. It
also allows more features to be added in the future, potentially by 3rd
party plugins.
The Client constructor now makes sure that the handshake object it's
given is valid. Also, the constructor is now exposed to the world
through the `panic.Client` property.
Addressing another panic pain point: you have to jump through insane,
unintuitive hoops just to access a single, non-dynamic client.
Useful for picking out clients and running code on JUST one, without
needing dynamic exclusion lists and `.pluck`.
