coment_rewrite interface example

test.cpp

World world;
EntityManager& em = *world.getManager<EntityManager>();
ComponentManager& cm = *world.getManager<ComponentManager>();

Entity e = em.createEntity();

auto positionMap = cm.getEntityMap<Position>();
auto velocityMap = cm.getEntityMap<Velocity>();
auto radiusMap = cm.getEntityMap<Radius>();
auto moverMap = cm.getEntityMap<Position, Velocity>();
auto circleMap = cm.getEntityMap<Position, Radius>();

cm.addComponent<Position>(e);    // positionMap now contains entity
cm.addComponent<Velocity>(e);    // positionMap, velocityMap, moverMap now contain entity
cm.removeComponent<Position>(e); // now only velocityMap contains entity
cm.addComponent<Radius>(e);      // now positionMap, radiusMap, and circleMap contain entity