rgb<->hsv alternative converter + some minor methods
filters: more transparency support
complex update for advanced format support via FreeImage lib
frame count in info method
migrated vignette to HSV domain
refactoring: use channel number verbose constants
added transparency flattener for 24bit output
slightly optimized transparency flattener
hack for freeimage older than 3.16
std=c89 support
added libm to config
added instruction for advanced io install
ascii output format
GIF loader: handled subframe sizes
usage.md update