Added currentpoly option

[christianmeichtry]

Now you can edit an existing polygon instead of only creating new ones. Pass the polygon you want to edit as currentpoly

      SM = PolySnapper({
        map: map,
        marker: new google.maps.Marker(),
        threshold: 200,
        keyRequired: false,
        polygons: polygons,
        polystyle: new_polystyle,
        hidePOI: true,
        currentpoly: edit_polygon,
        onEnabled: function(){
          console.log("enabled")
        },
        onDisabled: function(){
          console.log("disabled")
        }
      });