Function setRelativeInterval

setRelativeInterval(callback, interval): number
Sets an interval that fires at the given interval with respect to when it was fired.
```
const start = Date.now(); // 5555

// interval fires every second
setAbsoluteInterval(()=>{
	const now = Date.now();
	console.log(`${now}: FIRED`);
}, 1000);

// ideal output:
// 6555: FIRED
// 7555: FIRED
// 8555: FIRED
// etc...
```
Parameters
- callback: CustomIntervalCallback
  A callback that is fired on the interval.
- interval: number
  The interval to fire the callback at.
Returns number
An ID that tracks this interval.
- Defined in interval.ts:83