Implement oklab, oklch color space conversion functions, add example, restructure comments in the shaderlib, implements #37

examples/oklab.gdshader

@@ -0,0 +1,12 @@
+shader_type canvas_item;
+
+#include "res://shaderlib/colorspaces.gdshaderinc"
+
+//!load ./images/swamp.jpg
+
+void fragment() {
+	vec4 oklab = rgb2oklab(COLOR);
+	vec4 oklch = oklab2oklch(oklab);
+	oklch.z -= 2.0;
+	COLOR = oklab2rgb(oklch2oklab(oklch));
+}