Iteration progress used to be shown

[AmysFantasies]

This is similar to #39 and maybe will end up getting merged but while that issue requests that process be shown, I'm requesting that it be re-added. I actually compiled zopflipng back in either 2014 or 2015 on a previous PC and when using --filters with multiple strategies I very clearly remember zopflipng specifying the size for each filter as it went along. Now with a version I compiled today I get absolutely nothing except the final size, not even which strategy of those specified was chosen.

This is a serious deficiency for the way I use zopflipng. Knowing the size each filter strategy came out to helps me know whether PNGOUT's adaptive strategy (which is quite similar to zopflipng's entropy strategy in my experience) may be of use, and which strategies are no-hopers and can be discarded in runs where I use progressively greater iteration counts. Without knowing what each filter strategy came out to I can't do either of these things, and from my perspective I could do them with zopflipng up until a few weeks ago when I stopped using my old PC. I could cover all bases by using all strategies all the time, but the developers of zopfli should know better than anyone how slow it works and how useful being able to dump no-hoper strategies is to actually getting use out of this program.

So I'm opening this as a new issue because this is clearly a regression as I see it. While I could get the information I want by using the (undocumented) --verbose switch, this shows the results of each iteration for each strategy, outputting such a tsunami of data to dig through that would get ridiculous at high iteration counts. I could in theory do that anyway, but as I said I know for a fact that zopflipng did once simply output the final result of each strategy and, though I can't find it myself, the code for that must exist somewhere in the history of this repository. So I request that this be considered a regression and that this partial verbosity be somehow re-enabled, possibly as a command-line switch of some variety.