RFC for removing integer inference fallback

Rust infers primitive integer types, but when it can't find a solution it currently defaults to `int`. This is often seen as a potential subtle footgun. This RFC describes how to remove the feature, per https://github.com/mozilla/rust/issues/6023.
Shouldn't enum discriminants be the smallest type that allows to represent them all? (with preference for either signed or unsigned, not sure)

Or maybe we could introduce integer range types, and then it could be the smallest range covering them all, with no ambiguity.