building upon #127, can we add an Error method to error types so that in our sdk's we can directly return the error instead of having to map it to error msgs manually.

e.g. following method in the sdk could be just removed if we had that.

func errorVariantToError(err abc.Error) error {
	switch {
	case abc.ErrorInputNotSupported() == err:
		return fmt.Errorf("input not supported")
	case abc.RuntimeError() == err:
		return fmt.Errorf("runtime error")
	case abc.InvalidInput() == err:
		return fmt.Errorf("invalid input")
	default:
		return fmt.Errorf("no error provided by host implementation")
	}
}

Another thing we could possibly do is to replace "-" with " " automatically (to make it more readable), but its just a nice to have item.