Losslessly compress Forestry png assets with PNGGauntlet

[PNGGauntlet](http://pnggauntlet.com/) optimizes png files losslessly, and is used by web developers for making websites as fast as possible. It takes some time to process, but it results in a smaller file, especially for smooth assets like Faithful32.

By throwing the Forestry folder in and waiting a few minutes the file size is down to 612 KB, less than half the original 1.6 MB!

Please let me know if you would like me to process some more folders or if this is a bad idea somehow.