Adding the future class which changes characteristics based on objects.

include/characteristic/characteristic.hpp

@@ -6,9 +6,14 @@
 
 using json = nlohmann::json;
 
+namespace character {
+    class BillyObjects;
+}
+
 namespace character::characteristic {
     class Characteristic {
     protected:
+        friend character::BillyObjects;
         using defaultValue = std::numeric_limits<std::int32_t>;
         mutable std::int32_t total{ defaultValue::max() };
         const std::uint32_t base{ 0 };