Several fixes to job queueing.

* The job module is renamed to payload.  Having the module have the same
  name as the decorator used to define jobs would cause "module object
  is not callable" errors

* Uniqueness of a job is now just True or False.  Being able to discern
  which passed value goes to which argument is impossible once the job
  function is loaded as it could be decorated in such a way that the
  argspec just knows about *args and **kwargs and nothing else.

  It should be possible to re-introduce the feature at some point
  but *only* for keyword arguments.
Allow for datetime and timedelta argument values.

Before this patch we were limited by the fact that JSON doesn't specify
how to serialize date/time/timedelta object out of the box, so the
default json python lib borks on datetime and timedelta objects.

With custom encoder/decoder classes and some begrudgingly accepted
dependencies we can now serialize them as ISO-8601 formatted strings
with prefixes to denote their "type".
Bump version to 0.3.2.