Add some docstrings
Specify all subcommand arguments by kwarg (except name)
Use a parent parser for global options

so they can be specified both before and after the subcommand.
Split the arg parser building out of main()

and better describe that the 1 return code means KeyboardInterrupt.
Support PrettyTable 0.6.1

by adapting to 0.6 API when set_field_align() is missing.