lodepng update

[Lutger]

lodepng, a smallish png codec, has been updated to incorporate modest
png-editing capabilities. I've made some small changes to the encoding
interface as well. 

http://www.dsource.org/projects/scrapple/wiki/LodePngLibrary

Some minor work still needs to be done, but it is mostly complete and
functional. 

Thanks to Stewart for bugfixes and help. Also, sorry that it took me so long
for these updates.