Method unsubscribe

cpp/examples/broker.cpp:183–189

        subscriptions_[s] = 0;
    }
    void unsubscribe(Sender* s) {
        DOUT(std::cerr << "Queue:    " << this << "(" << name_ << ") unsubscribe Sender: " << s << "\n";);
        // If we're about to erase the current subscription move on
        if (current_ != subscriptions_.end() && current_->first==s) ++current_;
        subscriptions_.erase(s);
        s->add([=]{s->unsubscribed();});
    }
};

// We have credit to send a message.