[feature request] Sort `mix hex.outdated` output by status in default output about hex

[supersimple]

IMO I could see two changes:

1. group the deps into statuses visually - possibly use a flag and keep the current view as default
2. add flags to filter by status mix hex.outdated --update-possible

Anyone else have strong opinions?

[wojtekmach]

Adding a sort option sounds good to me. I'd hold off on adding filter though as it's easy to grep:

$ mix hex.outdated | grep "Update possible"

[juhalehtonen]

I started putting together a PR for this at #1017 . Happy to hear thoughts on the general direction there before I take it forward (or not!) 🙂