Product (multiplication)

```
/**
*  Returns the product of some numeric properties and numeric constants
*
*  Example: 6 * 7 * 2 = 84
*
*  Usage:
*    a: 6,
*    b: 7,
*    c: 2,
*    d: product('a', 'b', 'c'), // 84
*    e: product('a', 'b', 'c', 2) // 168
*/
```

JSBin to play with: http://emberjs.jsbin.com/qutak/7/edit?js,output

If `_utils`  private I don't see a reason to export it.