Add color class

Add Palladium Unique and Shared defs
Make stb_image an internal dependency
Start some work on font loader

include/amethyst.hpp

@@ -3,6 +3,7 @@
 #include <amethyst/app.hpp>
 #include <amethyst/assets.hpp>
 #include <amethyst/c3d.hpp>
+#include <amethyst/color.hpp>
 #include <amethyst/image.hpp>
 #include <amethyst/iron.hpp>
 #include <amethyst/renderer.hpp>