refactor Brush to be used in shared_ptr

src/asset.cpp

@@ -128,6 +128,11 @@ std::string Asset::absolute(const std::string& path)
 #endif
 }
 
+bool Asset::is_asset(const std::string & path)
+{
+    return path.find("data/") != std::string::npos;
+}
+
 bool Asset::open(const char* path)
 {
     //LOG("Asset::open %s", path);