Logging

[tony]

To aid, I would propose we add logging to the package

1. job name, args, kwargs + generating ID
2. checking for lock
3. creating lock
4. clearing lock

By default, they'd be at a super-low logging level, e.g. DEBUG (or NOTSET?)

Additionally / optionally:

• pure python example of setting the logging levels, to stdout, etc.

  (this treads a bit into helping the user do what they could themselves as it's standard library, but I think that logging is actually configured/tweaked rarely enough its helpful to the user to see an example)

• setting a global baseline, e.g. CELERY_SINGLETON_LOG_LEVEL, comparable to DJANGO_LOG_LEVEL