ensure that add state follows naming conventions

demo/demo/main.cpp

@@ -43,7 +43,7 @@
 #include "rollball.hpp"
 
 static void setup_menu(fggl::App& app) {
-	auto *menu = app.add_state<fggl::scenes::BasicMenu>("menu");
+	auto *menu = app.addState<fggl::scenes::BasicMenu>("menu");
 
 	// add some menu items for the game states
 	menu->add("terrain", [&app]() {
@@ -98,8 +98,8 @@ int main(int argc, const char* argv[]) {
 
 	// our test states
 	setup_menu(app);
-    app.add_state<GameScene>("game");
-	app.add_state<demo::RollBall>("rollball");
+    app.addState<GameScene>("game");
+	app.addState<demo::RollBall>("rollball");
 
 	return app.run(argc, argv);
 }

include/fggl/app.hpp

@@ -103,7 +103,7 @@ namespace fggl {
 			int run(int argc, const char **argv);
 
 			template<typename T>
-			T *add_state(const Identifer &name) {
+			T *addState(const Identifer &name) {
 				static_assert(std::is_base_of<AppState, T>::value, "States must be AppStates");
 				return m_states.put<T>(name, *this);
 			}