add JQuery's Promise like abilities to ES6's Promise

ES6PromiseExt

const noChange = (promise, done, fail) => {
  promise.then(done, fail)
  return promise
}

if(Promise.prototype.done == undefined)
  Promise.prototype.done = function(fn){
    return noChange(this,fn)
  }
if(Promise.prototype.fail == undefined)
Promise.prototype.fail = function(fn){
  return noChange(this, undefined, fn)
}
if(Promise.prototype.always == undefined)
Promise.prototype.always = function(fn){
  return noChange(this, fn, fn)
}