Make Result<T, E> extensions use IResult instead

[DrHeinzDoofenshmirtz]

Hi.

I would like to propose that extensions for Result<T, E>, such Match depends on and uses IResult instead.

The reason is that it would then be possible to make a sub-class of Result<T, E>, for example called ResultE<T>, with a custom error type, which would still have all the extensions available.

This would allow the creation of Result types with baked-in custom error types, which I have also seen another active Issue about.