No longer silently panic when a command fails
Check that filename has changed and only run when there is a newer
filename
Write output directly to file rather than to stdout
Instead of manually downloading the Zim files with a torrent directly,
move them into an actual derivation so it can easily be built into the
resulting images. Also, write an updater script that can automatically
download the files, determine the latest versions for each type and each
language, and generate the hash key values for them
Greg Hellings