SDL_stretch - Stretch Functions For SDL

While hacking on UAE (the unix amiga emulator) I did develop a few stretching routines. I have been asking on the SDL mainling for any prior art but it seems that no one did wrap such routines into a library part that can be reused everywhere. Other projects are just game SDKs which tend to wrap such routines it into their own framework - instead of using vanilla SDL surface. Also, there are only rare pieces of assembler optimized routines. I took some of these as hints and created my own set of highly optimized routines pumped up with assembler - stretch-and-blit routines for SDL on steroids.