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/window/Window.h

@@ -57,6 +57,7 @@ public:
 		SETTING_CENTERED,
 		SETTING_DISPLAY,
 		SETTING_HIGHDPI,
+		SETTING_SRGB,
 		SETTING_MAX_ENUM
 	};
 
@@ -157,6 +158,7 @@ struct WindowSettings
 	bool centered; // = true
 	int display; // = 0
 	bool highdpi; // false
+	bool sRGB; // false
 
 }; // WindowSettings