function bottom(layout
/*: Layout*/
)
/*: number*/
{
  var max = 0,
      bottomY;

  for (var i = 0, len = layout.length; i < len; i++) {
    bottomY = layout[i].y + layout[i].h;
    if (bottomY > max) max = bottomY;
  }

  return max;
}
Return the bottom coordinate of the layout.

@param  {Array} layout Layout array.
@return {Number}       Bottom coordinate.