code: public static <A, B, C, D> Converter<Example<A, B>, Example<C, D>> converter(
        Converter<A, C> inputConverter, Converter<B, D> outputConverter) {
      return new ExampleConverter<A, B, C, D>(inputConverter, outputConverter);
    }
docs: Creates a converter which applies {@code inputConverter} to the input of
  each example, and {@code outputConverter} to the output.
  
  @param converter
  @return