[Feature Request] Reproducible builds

I would like to see "reproducible builds" for AppImages.

When I use *`appimagetool`* to convert an AppDir into an AppImage, the md5 or shaX hashes change after every run, even if the AppDir didn't change.

I think this has to do with some timestamps being automatically set to current by *`mksquashfs`*.

Is there a way to avoid this?

It would be very beneficial to only have changing md5/shaX hashes *if and only if* some "meaty" content of the AppDir changed!