论文：<<Real Time Bid Optimization with Smooth Budget Delivery in Online Advertising>>
介绍两个部分：
1、预估未来消耗率
2、基于消耗率和先验分布来挑选展现和调整bid
pacing-rate=bids/reqs
1、预估未来消耗率：pacing-rate
迭代计算：
pacing-rate(t+1) = pacing_rate(t)*reqs(t)*win_rate(t)/(reqs(t+1)*win_rate(t+1)) * S(t)/S(t+1)
