Improve match return types inference

[zoontek]

Fixes #89

I'm not a fan of the naming (B1, B2, etc.), but not a fan of the initial naming too (A, B).
But maybe is that OK for you? It could also be:

match<SomeReturnType, NoneReturnType = SomeReturnType>(
  this: Option<Value>,
  config: {
    Some: (value: Value) => SomeReturnType;
    None: () => NoneReturnType;
  },
): SomeReturnType | NoneReturnType {}

It will be verbose, but clearer.