Created by: cbjuan
As discussed in #519, #892 (closed) and across different commits, the Bull library lacks a method to process the queue consuming individual jobs instead of doing the same retrieving all the jobs available sequentially.
This PRs proposes a processOne method to do this task, allowing users to retrieve one job from the queue in each call for the function. To implement this, we have continued some methods yet available in Bull as described in https://github.com/OptimalBits/bull/issues/519#issuecomment-421407186, https://github.com/OptimalBits/bull/issues/519#issuecomment-422060733, and https://github.com/OptimalBits/bull/issues/519#issuecomment-422790555
@pacomf, @jelcaf and me co-author this PR.