Idiomatic Kotlin?

The first attempt to describe what idiomatic Kotlin means and how to attribute. Right now we have a bunch of idioms on the Kotlin language website, which I guess most of the who have come up from the team. That's the funny thing because there is no one body for deciding on what are English idiomi. So if you design code to be read by non-Kotlin developers, you will write it differently than when you know that those will be experienced Kotlin developers.