added a scheduler

currently its really pretty basic, and doesn't have much features.

example config:

    SCHEDULE = {
        'runs-every-10-seconds':{
            'task': 'tasks.echo',
            'schedule': timedelta(seconds=10)
        },
        'runs-every-10-minutes':{
            'task': 'tasks.foo',
            'schedule': timedelta(minutes=10)
        }
    }

    SCHEDULER_FILE_NAME = '/home/users/ybrs/scheduler'

then you can run scheduler with

    kuyruk --config=tasks.py --logging-level=debug scheduler

comments greatly appreciated.