Feat/config support

First cut at config file support, may well change before it is merged.  Just want to get it out there for testing.

At the very least expect more options to be exposed via the config file:

- [ ] verbosity (likely)
- [ ] coloured output toggling (likely)
- [ ] colour output theming (unlikely, but suggested by Nathan)
- [ ] subcommand defaults (likely)
- [ ] datetime format if I'm pushed hard enough (unlikely, but possible)