Auto restart configuration option #24

Problem

There is no easy way that existing countdowns restart automatically after they ended.

Solution

• Add a new auto_restart configuration option that restarts the countdown when done. Default should be false when not configured.
• Add a new start_countdown configuration option that allows you to configure a countdown key that gets started, by default current countdown when not configured.

Example

countdowns:
  example_event:
    type: DURATION
    duration: "1d"
    auto_restart: true
    start_countdown: "other_countdown"
  other_countdown:
    ...