Added sRGB (gamma-correct) support for Images, Canvases, and the main screen.

love.graphics.newImage(path, “srgb”) creates a new Image whose texels are treated as being in the sRGB color space, so they are linearized when drawing/sampling from the image.

love.graphics.newCanvas(w, h, “srgb”) creates a new Canvas whose texels are treated as being in the sRGB color space, so drawing to the Canvas does a linear->sRGB conversion (but blends linearly), and sampling from it (drawing it or using it in a shader) converts from sRGB to linear space.

The "srgb" window flag does the same as Canvases for the main screen.

src/modules/graphics/opengl/wrap_Canvas.h

@@ -39,7 +39,7 @@ int w_Canvas_renderTo(lua_State *L);
 int w_Canvas_getImageData(lua_State *L);
 int w_Canvas_getPixel(lua_State * L);
 int w_Canvas_clear(lua_State *L);
-int w_Canvas_getType(lua_State *L);
+int w_Canvas_getFormat(lua_State *L);
 int w_Canvas_getFSAA(lua_State *L);
 extern "C" int luaopen_canvas(lua_State *L);