Version overloading

This is an issue for discussion of version overloading proposal. The full text of the proposal is [here](https://github.com/Kotlin/KEEP/blob/version-overloading-proposal/proposals/version-overloading.md). Please use this issue for the discussion on the substance of the proposal. For minor corrections to the text, please open comment directly in the PR https://github.com/Kotlin/KEEP/pull/423.