Butano `bn::pool` example

#include <bn_core.h>
#include <bn_forward_list.h>
#include <bn_log.h>
#include <bn_pool.h>

struct Bullet {
    int x, y;
    bool is_dead;
};

int main() {
    bn::core::init();
    constexpr int POOL_SIZE = 2;

    bn::pool<Bullet, POOL_SIZE> bullet_pool;
    bn::forward_list<Bullet*, POOL_SIZE> bullet_list;

    // Create bullets in `bullet_pool`, store their pointers to `bullet_list`.
    Bullet& bullet1 = bullet_pool.create(11, 11, true);
    Bullet& bullet2 = bullet_pool.create(22, 22, true);
    bullet_list.push_front(&bullet1);
    bullet_list.push_front(&bullet2);

    BN_LOG("bullet1 created on {x=", bullet1.x, ", y=", bullet1.y, "}");
    BN_LOG("bullet2 created on {x=", bullet2.x, ", y=", bullet2.y, "}");

    // Destroy the dead bullets
    bullet_list.remove_if([&bullet_pool](Bullet* bullet) -> bool {
        if (bullet->is_dead) {
            BN_LOG("Destroy bullet on {x=", bullet->x, ", y=", bullet->y, "}");
            bullet_pool.destroy(*bullet);
            return true;
        }
        return false;
    });

    // Now that the `bullet_pool` is empty, you can push 2 bullets again.
    bullet_list.push_front(&bullet_pool.create(42, 42, true));
    bullet_list.push_front(&bullet_pool.create(99, 99, true));

    for (const Bullet* bullet : bullet_list)
        BN_LOG("bullet created on {x=", bullet->x, ", y=", bullet->y, "}");

    // Another way to conditionally destroy.
    for (auto before_iter = bullet_list.before_begin(),
              iter = bullet_list.begin();
         iter != bullet_list.end();) {
        Bullet* bullet = *iter;
        if (bullet->is_dead) {
            BN_LOG("Destroy bullet on {x=", bullet->x, ", y=", bullet->y, "}");
            bullet_pool.destroy(*bullet);
            iter = bullet_list.erase_after(before_iter);
        } else {
            before_iter = iter;
            ++iter;
        }
    }

    BN_LOG("bullet_list.size(): ", bullet_list.size());
    BN_LOG("bullet_pool.size(): ", bullet_pool.size());

    while (true)
        bn::core::update();
}