update pbar by Real-Time speed

[githubyong]

It seems that the speed is an average data,and then the ETA() will not exact.
How about update the progress bar by real-time speed,and calculate ETA() by real-time speed ?

[NiltonVolpato]

What do you mean? ETA uses the wall time, there's also AdaptiveETA, which may be more accurate if the time to perform each operation varies