Fixes #50 (config slice does not return help)

This commit changes the config slice so that it is up to date with the other slices (using the new-style "slice_commands" method to setup the commands supported by this slice and adding support for the "-h" and "--help" flags (to get help on the usage of this slice)
Merge pull request #55 from tjmcs/tb/return-help-from-config

Fixes #50 (config slice does not return help)