Increasing the time limit of the communication test.

In some testing environment it caused problems.
Pep8.
Use only new-style classes.
Changed JSONDecodeError to ValueError.

It is needed after moving from simplejson to json.
Adapt some pydoc to the correct format for raises.
Changed class to type when appropriate in the pydoc.
Timestamps are now in datetime.
Digests are really unicode strings.
Some pylint fixes.
Added some docstrings to Job.
Improvements on pydoc types.