Adaptive resize

10x for lwip! you should name it natimg :) so it maintains a bit about the confusion with the other lwip project. :)

Needed this func. in some nw project, ported from https://github.com/smottt/WideImage/blob/master/lib/WideImage/Operation/Resize.php

Note: I think theres a problem with resizing (the native lib part) on this branch, as is forked from feature/gif.
Anyway, modifs are working for me in nw, based on 0.0.5 branch, but i didn't see any point in uploading that, as you obviously optimized your code for the new release. (also updated decree to 6 in 0.0.5 to declare the custom type)

cheers!