Added initWithPath: to better facilitate multiple queues.

[spazision]

EDQueue doesn't support assigning priorities to jobs. The easiest workaround IMO is multiple queues, where the "low priority" jobs (which are assumed to be more numerous) are put into the sharedInstance() queue, and the "high priority" jobs (which are assumed to be less numerous) are put into a custom instance with a different path.

[cbh2000]

Duplicate of #9. Probably better to add priorities to queue internally, but this is a good workaround in the mean time.