added validity check upon opening a file
cleanups, refactored repetitive stuffs
minor cleanups
added paletted png save support (transparency needs work, currently locked to 4 levels)
corrected wrong checkbox defaults in PngOptions
paletted png save has arbitrary alpha levels now
enabled interlace support (buggy, saving progress)
trying to fix offset bug where left/top edges wont wrap properly to other sides, (saving progress)
fixed clipping bug, was messing up offset tool
fixed clipping bug, was messing up offset tool
interlaced png support, gamma support removed
used a vector instead of png_malloc, minor cleanups also
minor cleanups