5.1.0

Added

• kranfix: Option<Result<T, E>>.transpose() returns a Result<Option<T>, E>.
• kranfix: Option<Option<T>>.flatten() returns an Option<T>.
• kranfix: Result<Option<T>, E>.transpose() returns an Option<Result<T, E>>.
• kranfix: Result<Result<T, E>, E>.flatten() returns a Result<T, E>.