HX711 library for Mongoose OS

This is my attempt at adapting the arduino-hx711 library into a native mongoose os one.

Example code for JS

load('api_config.js');
load('api_events.js');
load('api_gpio.js');
load('api_mqtt.js');
load('api_net.js');
load('api_sys.js');
load('api_timer.js');
load('api_arduino_hx711.js');
let dataPin = 12;
let clkPin=14;

let sensor = HX711.init(dataPin, clkPin, 128);

// Print reading every second
Timer.set(1000 /* 1 sec */, Timer.REPEAT, function() {
  let value = sensor.read_average(4);
  print('HX711: ', value);
}, null);