Refactor engine code

Engine/loader/mesh.h

@@ -0,0 +1,15 @@
+#pragma once
+
+#include <string>
+#include <vector>
+#include <map>
+#include "renderer.h" // includes Vec3, Vec2, Triangle, Color
+
+struct Material
+{
+    Color color;
+    std::string texture_path;
+};
+
+std::map<std::string, Material> load_mtl_materials(const std::string& mtl_path);
+std::vector<Triangle> load_obj(const std::string& obj_path, Renderer* renderer);