Support conversion to Either

[shadowhand]

Would it make sense to have a Maybe::toEither(): Either method?

abstract class Maybe
{
    // ...
    public function toEither(): Either
    {
        return $this->map('\PhpFp\Either\Either::of')->fork(Either::left(null));
    }
}

Or perhaps it would be better to have abstract public function toEither(): Either implemented as:

// Just
public function toEither(): Either
{
    return Either::of($this->value);
}

// Nothing
public function toEither(): Either
{
    return Either::left(null);
}