v0.4.0 Scheduling

This release adds --later, the ability to buffer a task for later.

Warning: This release shifts the priority keys down one. I.E., priority 4 is now 3, and 1 is now 0. All you need to do is reassign the priority with --priority.

Any config issues can be resolved with --config

Also, the pre-release classifier has been bumped up to production.