Converted David Ludwig's D3D11 renderer to C and optimized it.

The D3D11 renderer is now slightly faster than D3D9 on my Windows 8 machine (testsprite2 runs at 3400 FPS vs 3100 FPS)
This will need tweaking to fix the Windows RT build.

CMakeLists.txt

@@ -799,11 +799,12 @@ elseif(WINDOWS)
     endif()
     set(CMAKE_REQUIRED_FLAGS "/I\"$ENV{DXSDK_DIR}\\Include\"")
     check_include_file(d3d9.h HAVE_D3D_H)
+    check_include_file(d3d11_1.h HAVE_D3D11_H)
     check_include_file(ddraw.h HAVE_DDRAW_H)
     check_include_file(dsound.h HAVE_DSOUND_H)
     check_include_file(dinput.h HAVE_DINPUT_H)
     check_include_file(xaudio2.h HAVE_XAUDIO2_H)
-    if(HAVE_D3D_H OR HAVE_DDRAW_H OR HAVE_DSOUND_H OR HAVE_DINPUT_H OR HAVE_XAUDIO2_H)
+    if(HAVE_D3D_H OR HAVE_D3D11_H OR HAVE_DDRAW_H OR HAVE_DSOUND_H OR HAVE_DINPUT_H OR HAVE_XAUDIO2_H)
       set(HAVE_DIRECTX TRUE)
       # TODO: change $ENV{DXSDL_DIR} to get the path from the include checks
       link_directories($ENV{DXSDK_DIR}\\lib\\${PROCESSOR_ARCH})
@@ -844,6 +845,10 @@ elseif(WINDOWS)
       set(SDL_VIDEO_RENDER_D3D 1)
       set(HAVE_RENDER_D3D TRUE)
     endif()
+    if(RENDER_D3D AND HAVE_D3D11_H)
+      set(SDL_VIDEO_RENDER_D3D11 1)
+      set(HAVE_RENDER_D3D TRUE)
+    endif()
     set(HAVE_SDL_VIDEO TRUE)
   endif()