New script: prioritize - monitors job creation and boosts priority for configurable job types

[myk002]

The prioritize script sets the do_now flag on all of the specified types of jobs that are currently ready to be picked up by a dwarf. This will force them to complete the jobs as soon as possible. This script can also continue to monitor creation of new jobs and automatically boost the priority of newly created jobs of specific types.

This is most useful for ensuring important (but low-priority -- according to DF) tasks don't get indefinitely ignored in busy forts. The list of monitored job types is cleared whenever you load a new map, so you can add a line like the one below to your onMapLoad.init file to ensure important job types are always completed promptly in your forts:

    prioritize -a StoreItemInVehicle PullLever DestroyBuilding RemoveConstruction RecoverWounded FillPond DumpItem SlaughterAnimal

This implementation uses the eventful plugin to hook the creation of jobs so it can automatically modify new jobs. It cleans up after itself and unregisters the callbacks when no tracked job types remain (or when a map is unloaded).

[myk002]

docs are failing because I pre-emptively refer to do-task-now from #316

edit: removed reference to #316 for now. I can add it back once both scripts are merged.