Add function to set variants for a species, and a function to get the count of species in a species library.

src/Library/SpeciesLibrary.hpp

@@ -26,6 +26,8 @@ namespace CreatureLib::Library {
 
         void LoadSpecies(const std::string& name, const CreatureSpecies* species);
         void DeleteSpecies(const std::string& name);
+
+        size_t GetCount() const { return _species.count(); }
     };
 }