I want a directive to re-render HTML whenever three scope variables have changed. The first two are just integers, the third is an array.

We have `$watchGroup` to watch several variables, we have `$watch` with `objectEquality` as a third parameter, and we have `$watchCollection` which is like `$watch`, but with `objectEquality` implied.

Is there a way to write a `$watch` similar to this?

```
$scope.$watchGroup(['number1', 'number2', 'myArray'], callback, true); // true for objectEquality

```