Mark destructors of several libraries as virtual.

src/Library/SpeciesLibrary.hpp

@@ -14,7 +14,7 @@ namespace CreatureLib::Library {
         SpeciesLibrary(size_t initialCapacity = 32)
             : _species(std::unordered_map<std::string, const CreatureSpecies*>(initialCapacity)){};
 
-        ~SpeciesLibrary() {
+        virtual ~SpeciesLibrary() {
             for (auto s : _species)
                 delete s.second;
             _species.clear();