Idea: neil dep upgrade

[teodorlu]

Original Slack thread on #babashka-neil: https://clojurians.slack.com/archives/C03KCV7TM6F/p1660304001426249

Proposed API:

neil dep upgrade - upgrades all dependencies to the latest version
neil dep upgrade --dry-run - shows all available upgrades
neil dep upgrade --lib hiccup/hiccup - upgrades only hiccup
neil dep upgrade --dry-run --lib hiccup/hiccup - shows available upgrades for hiccup

[teodorlu]

We could possibly allow listing several libraries:

neil dep upgrade :lib LIBRARY_1 :lib LIBRARY_2

But I'm not sure whether that would cause problems for the global :lib option spec.

[borkdude]

For now let's not add more stuff to the issue, and focus on what's described in the first post.