feat(config): accept mail configuration options (#244)
feat(config): accept mail configuration options (#244)

refs #232, #216

- this is the most straight forward pass through adding mail config options
- there is loads of small tweaks possible here, but they are not required
E.g.
- auto-set transport to smtp if any other argument is supplied
- use grouping to make the output better
- stronger use of implies?
TryGhost/Ghost-CLI,TomChantler/Ghost-CLI