Refactor CLI organisation, and improve termination

[XAMPPRocky]

As part of what we discussed in #555 we want to improve the CLI of run to be better, as part of that to make code for the commands more easily maintainable, I've first gone ahead and done a small refactor that moves each command into its own file and implementing them as their own types with a method to run them. This improves locality by a lot as now everything related to one command exists entirely in that one file.

The only actual changes in this PR are the following.

• In src/main.rs we now catch the result ourselves and ensure to emit it as a tracing::error, using the Display formatting before exiting with a non-zero error code. Previously it would use the Debug formatting and output to stdout.
• We now expose a Cli type from the library that can be used to drive the application, as opposed to exposing run and manage as free functions.

[bombsimon]

LGTM! 🧹

[quilkin-bot]

Build Succeeded 🥳

Build Id: 37168eb6-6ba6-441b-a219-7246e2dfb0c0

To build this version:

git fetch git@github.com:googleforgames/quilkin.git pull/570/head:pr_570 && git checkout pr_570
cargo build