implemented CRTP shader on ColorShader and Rectangle

shaders/shaderbase.cpp

@@ -7,11 +7,11 @@
 #include "../buffer.cpp"
 
 namespace UwU {
-  template <typename Derived>
+  template <class ShaderT>
   class ShaderBase {
     public:
       Color shade(uint16_t x, uint16_t y) {
-        return static_cast<Derived*>(this)->shade(x, y);
+        return static_cast<ShaderT*>(this)->shade(x, y);
      }
   };
 }