code: function(index)
    {
      var key = this.keys[ index ];
      var lastValue = AP.pop.apply( this.values );
      var lastKey = AP.pop.apply( this.keys );
  
      if ( index < this.values.length )
      {
        this.values[ index ] = lastValue;
        this.keys[ index ] = lastKey;
        this.indices[ lastKey ] = index;
      }
  
      delete this.indices[ key ];
  
      return this;
    }
docs: Removes the value & key at the given index.
  
  @param {Number} index
  @return {Rekord.Map} -
  The reference to this map.