clear_waiting() function to clear the waiting queue.
Added stop_on_lane_error parameter to ezpq.Job to allow for short-circuiting a synchronous lane if a job in the lane fails. When set to True and the preceding job has a non-zero exit code, this job will not be run. Note that this is to be set per-job for flexibility.
stop_all() function now clears the waiting queue and terminate running jobs. This addresses a bug where a queue would fail to close when disposing with jobs still in the waiting queue.
The default poll for the queue itself is still 0.1. Now, the default poll for get and wait is equal to the poll for the queue itself, as it makes no sense to check for changes more freqeuntly than changes could arise.