SDL graphics drawing primitives and support functions

<rendered-html><p>The SDL_gfx library evolved out of the SDL_gfxPrimitives code which provided basic drawing routines such as lines, circles or polygons and SDL_rotozoom which implemented a interpolating rotozoomer for SDL surfaces.</p> <p>The current components of the SDL_gfx library are:</p> <ul> <li>Graphic Primitives (SDL_gfxPrimitves.h)</li> <li>Rotozoomer (SDL_rotozoom.h)</li> <li>Framerate control (SDL_framerate.h)</li> <li>MMX image filters (SDL_imageFilter.h)</li> <li>Custom Blit functions (SDL_gfxBlitFunc.h)</li> </ul> <p>The library is backwards compatible to the above mentioned code. Its is written in plain C and can be used in C++ code.</p> </rendered-html>