code: public static <T1, T2, R> FluentFunctions.FluentBiFunction<T1, T2, R> of(final BiFunction<T1, T2, R> fn) {
          return new FluentBiFunction<>(
                                        fn);
      }
docs: Convert a BiFunction to a FluentBiFunction
  <pre>
  {@code
  CompletableFuture<Integer> cf = FluentFunctions.of(this::add)
  .liftAsync(ex)
  .applyHKT(1,1)
  
  }
  </pre>
  @param fn BiFunction to convert
  @return FluentBiFuntion