Add the ability to specify RunLoop and RunLoopMode in `after` and `every` methods

[madeinqc]

This was required in my project to be able to use after and every methods for timers that need to update the UI. The timer needs to run in .commonModes to be able to update the UI while scrolling.

It keep the same behaviour as previously and the signature is backward compatible. I added a new start function because the splat operator is not available in Swift, hence the need to create a new one that takes an array as parameters.

Feedbacks are welcome, I will adjust the PR accordingly.