added possibility to use multiple filters
added possibility to use multiple filters

liangzeng/node-png,lukeapage/pngjs2,gagern/pngjs2,sapphire-al2o3/node-pngjs,neophob/pngjs2,dokipen/node-pngjs,neophob/pngjs2,gagern/pngjs2,lukeapage/pngjs2