refactor Brush to be used in shared_ptr

src/asset.h

@@ -11,7 +11,7 @@ public:
     static bool exist(std::string path, bool is_asset);
     static bool delete_file(const std::string& path);
     static std::string absolute(const std::string& path);
-
+    static bool is_asset(const std::string& path);
     std::string m_current_path;
     FILE* m_fp = nullptr;
     int m_len = 0;