Knocked out an important TODO: Parameterize Job.GetAsync and Job.TransitionAsync strategy.

See the XML Documentation. Briefly, it's the usual sort of thing:
* Linear or non-linear time between retries?
50% increase on each retry
* How long before first retry?
Default: 250 milliseconds.
* How many retries?
We retry for a specified number of milliseconds using a
CancellationSource and a CancellationToken. Default: 30 seconds
* Should we cancel the job, if it times out?
No, but of course we do provide a Job.Cancel method.
Removed TODO from source code