Job scheduling

[robson-gupy]

I implemented a job scheduler as crontab. I needed to change the interval behavior. Now the interval attribute is not required, because you may use cron.

Example of configuration

<source>
  ...
  cron            0 9 * * *           # Run at 9 am
  ...
</source>

I used rufus-scheduler to schedule job.

[y-ken]

Hi @robsonvnt
Thank you for your pull request. I'll review them soon!
It's coming right interval query execution.