Display update changelog if requested on `self-update`

[CompeyDev]

This can potentially be expanded to display changelogs for updates on all tools, rather than just Rokit itself.

Closes #19.

[CompeyDev]

I am slightly concerned about the diff in Cargo.lock though

I played around with the features for mdcat - but it doesn't improve the changes in Cargo.lock much. There aren't any features on mdcat to disable HTTP requests either. By itself, mdcat isn't much of a library, but more of a CLI tool, which has a library interface too.

I can probably swap it out for another markdown renderer, but I've not found any other alternatives to have satisfactory render outputs.

[filiptibell]

It seems like mdcat is mostly a light wrapper around pulldown-cmark-mdcat, and that crate has features for these large dependencies that can be disabled. Maybe we can use that directly instead? Or if all else fails, we could do some very rudimentary markdown rendering of our own using a simpler parser-only markdown crate. I don't think we're going to have release changelogs with anything beyond basic headers and lists for Rokit anytime soon, at least 😄

[CompeyDev]

Maybe we can use that directly instead?

I currently am already disabling its features - but I'll try seeing if using it as a direct rather than peer dependency makes any difference.

[filiptibell]

I currently am already disabling its features - but I'll try seeing if using it as a direct rather than peer dependency makes any difference.

Yeah, you'll have to remove mdcat since it uses default (all) features for that crate. The cargo book section on feature unification clarifies this a bit - features are always treated as additive and any one of your other dependencies enabling them will mean that they're enabled across the board