Add “mkinitcpio” step
Simplify unnecessary Python workarounds

* Saving open() result before “try” block does not lose any exception
  handling
* itemgetter() not needed to sort dictionary items because the keys are
  never equal, thus the values will never be compared
Split apart long lines
Fixes for Python 3
Fix field misnaming
Replace lib.run_main() with “argparse” implementation
Drop Python < 3.3 support