code: function indexOf(arr, x, comparator)
  {
    var cmp = comparator || equalsStrict;
  
    for (var i = 0, n = arr.length; i < n; i++)
    {
      if ( cmp( arr[i], x ) )
      {
        return i;
      }
    }
  
    return false;
  }
docs: Finds the index of a variable in an array optionally using a custom
  comparison function. If the variable is not found in the array then `false`
  is returned.
  
  ```javascript
  Rekord.indexOf([1, 2, 3], 1); // 0
  Rekord.indexOf([1, 2, 3], 4); // false
  Rekord.indexOf([1, 2, 2], 2); // 1
  ```
  
  
  @memberof Rekord
  @param {Array} arr
  The array to search through.
  @param {Any} x
  The variable to search for.
  @param {Function} [comparator]
  The function to use which compares two values and returns a truthy
  value if they are considered equivalent. If a comparator is not given
  then strict comparison is used to determine equivalence.
  @return {Number|Boolean} -
  The index in the array the variable exists at, otherwise false if
  the variable wasn't found in the array.