Scheduler v1.3

Version 1.3 of our simple message queue Scheduler is now available. This release comes with a couple improvements and should be considered mandatory for any production workloads due to database performance improvements.

• Add indices for various fields used for searching and filtering, should improve performance on sites with a large history substantially [#25]
  
• Add task_key field to sTaskRun, to allow setting/searching/indexing of small pieces of data. Among other things, this allows outside extras to retrieve and act on task runs more easily.
  
• Track the processing time of task runs [#20]
  
• Add optional automatic cleanup of old tasks. Set the scheduler.delete_tasks_after system setting to a value like "-1 year" or "-2 weeks" to remove completed and failed tasks older than that.

Note that if you already have hundreds of thousands of task runs, the upgrade may be a little slow (in the range of 10-20 seconds) to add the new indices.