function polygonAppend(polygon, poly, from, to){
    for(var i=from; i<to; i++){
        polygon.push(poly[i]);
    }
}
Append points "from" to "to"-1 from an other polygon "poly" onto this one.
@method append
@param {Polygon} poly The polygon to get points from.
@param {Number}  from The vertex index in "poly".
@param {Number}  to The end vertex index in "poly". Note that this vertex is NOT included when appending.
@return {Array}