Allow job ID to be set on enqueue/enqueue_call() - fixes #412
Added better job ID tests
Forced job_id to only allow str/unicode
Fixed bug with format() in py3
Renamed job_id to id, and fixed py3 bug, per #415
Fixed another py3 bug - my bad. Also moved type checking further down
Fixes from comments in #415
Added tox/vagrant tmp dir to gitignore
Removed unused import
Renamed id to job_id in enqueue_call() as per comments in #415
Fixed silly typo
Another unused import, oops
Merge pull request #415 from foxx/feature/custom-job-ids

Allow job ID to be set on enqueue/enqueue_call() - fixes #412