code: function BunnyFormData(form) {
      if (!(form instanceof HTMLFormElement)) {
          throw new Error('Form passed to BunnyFormData constructor is not an instance of HTMLFormElement');
      }
  
      // form
      this._form = form;
  
      // form control collection;
      this._collection = {};
  
      // build collection from form elements
      var elements = this.getInputs();
      for (var k = 0; k < elements.length; k++) {
          var input = elements[k];
          this._initSingleInput(input);
      }
  }
docs: FormData wrapper for browsers supporting only FormData constructor and append()
  Instead of keys(), entries(), values() have getAllElements()
  Instead of delete() -> remove()
  To get real FormData object use buildFormDataObject()
  Also adds custom methods