Introduce `RsResult` - our equivalent of Rust's Result in Kotlin
Introduce `RsResult` - our equivalent of Rust's Result in Kotlin

It's called `RsResult` instead of `Result` because there is
`kotlin.Result` in the Kotlin stdlib and it is imported by default

Our equivalent to Rust's `result?` (or `try!(result)`) is
`result.unwrapOrElse { return Err(it) }`

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