Working on save-load system and UI

src/ISaveable.h

@@ -0,0 +1,12 @@
+#pragma once
+#include "external/nlohmann/json.hpp"
+
+namespace ZL {
+
+struct ISaveable {
+    virtual void save(nlohmann::json& out) const = 0;
+    virtual void load(const nlohmann::json& in) = 0;
+    virtual ~ISaveable() = default;
+};
+
+} // namespace ZL