Request: Several new flags similar to those used by jpegoptim

[mgrhm]

I've used jpegoptim quite extensively in the past with good results. guetzli's level of compression is far superior, but it's missing a few of the features which make jpegoptim such a good tool.

There are three specific flags I use a lot which would bring guetzli closer to feature parity without adding too much complexity.

They are (quoted from the jpegoptim man page:

-o, --overwrite
Overwrite target file even if it exists (when using -d option).

-p, --preserve
Preserve file modification times.

-t, --totals
Print totals after processing all files.

Adding these as flags wouldn't affect guetzli's default behaviour, so those using it already could continue to do so. They would increase the usefulness of the tool significantly.

I'd also like a flag to preserve EXIF data, but this is already open in ticket #161 so I won't duplicate the request here.

[gtuk]

#171

[gtuk]

#175

[mgrhm]

Thanks @gtuk for the work you're doing on this.