This actually ends up being faster than Direct3D with a dynamic texture. (???)

Also experimented with dynamic textures, but didn't get any speed increase with them.  More research and testing is needed.

Also experimented with texture rectangle updates, but I think at this point the full rect update gives the most consistent results.

Switched the SDL 1.2 compatibility to use the window surface, so it's fast even when there's no hardware acceleration available.
This means that the YUV overlay now uses software, but that's okay since fast YUV code should be using the textures now anyway.

Added a way to get a framebuffer interface for a window, and also a way to create a software renderer for an arbitrary surface.
The software renderer has been re-routed to use the framebuffer interface, which makes it possible to have software rendering available even on simple ports.

--HG--
rename : src/video/SDL_blendline.c => src/render/software/SDL_blendline.c
rename : src/video/SDL_blendpoint.c => src/render/software/SDL_blendpoint.c
rename : src/video/SDL_draw.h => src/render/software/SDL_draw.h
rename : src/video/SDL_drawline.c => src/render/software/SDL_drawline.c
rename : src/video/SDL_drawpoint.c => src/render/software/SDL_drawpoint.c

This allows me to reduce the set of formats supported by the renderers to the most optimal set, for a nice speed boost.

--HG--
rename : src/video/SDL_yuv_mmx.c => src/render/SDL_yuv_mmx.c
rename : src/video/SDL_yuv_sw.c => src/render/SDL_yuv_sw.c
rename : src/video/SDL_yuv_sw_c.h => src/render/SDL_yuv_sw_c.h
rename : src/video/mmx.h => src/render/mmx.h

Moved the rendering code out to a separate directory in the hope that it can someday be completely decoupled from the rest of the library and be expanded to an awesome 2D on 3D library.

--HG--
rename : src/video/windows/SDL_d3drender.c => src/render/direct3d/SDL_d3drender.c
rename : src/video/SDL_renderer_gl.c => src/render/opengl/SDL_renderer_gl.c
rename : src/video/SDL_renderer_gles.c => src/render/opengles/SDL_renderer_gles.c
rename : src/video/SDL_renderer_sw.c => src/render/software/SDL_renderer_sw.c

The rendering functions take a context so it's clear what window they're drawing to.  This also potentially opens to the door to multi-threaded rendering in the future.