message: add bindvalue for multiselect
diff: @@ -78,7 +78,7 @@ export class NgSelectComponent implements OnInit, OnChanges, ControlValueAccesso
  filterValue: string = null;
  - private _value: NgOption = null;
  + private _value: NgOption | NgOption[] = null;
  private _openClicked = false;
  private propagateChange = (_: NgOption) => { };
  @@ -350,7 +350,10 @@ export class NgSelectComponent implements OnInit, OnChanges, ControlValueAccesso
  if (!this._value) {
  this.propagateChange(null);
  } else if (this.bindValue) {
  - this.propagateChange(this._value[this.bindValue]);
  + const bindValue = this._value instanceof Array ?
  + this._value.map(x => x[this.bindValue]) :
  + this._value[this.bindValue];
  + this.propagateChange(bindValue);
  } else {
  this.propagateChange(this._value);
  }
  