Renamed close_asset to unload_asset

include/GameEngine.h

@@ -40,7 +40,7 @@ void remove_object(ObjectID *id);
 
 // ASSET MANAGEMENT API
 AssetID load_asset(const char *path, AssetType type);
-void close_asset(AssetID *id);
+void unload_asset(AssetID *id);
 // END ASSET MANAGEMENT API
 
 // RENDERING API