Add example program: color palette

Sliders for many color spaces update as any other sliders are moved
around. Color is space is clamped to sRGB, so Lab and Lch color spaces
cannot be fully expressed.

TODO:
- Real-time manipulation of base color to create a color scheme.
- Show slider value under each slider
- Show output values in text boxes for each color space

Cargo.toml

@@ -41,6 +41,7 @@ members = [
     "winit",
     "examples/bezier_tool",
     "examples/clock",
+    "examples/color_palette",
     "examples/counter",
     "examples/custom_widget",
     "examples/download_progress",