Add support for mini.nvim

[tjkuson]

Hi, here's my attempt at adding explicit support for mini.nvim.

I started by patching mini.pick and mini.files which are unusable on master (the colours for selected and unselected items are the same, making it impossible to tell what's selected). I then decided to add support for the rest of the plugins.
As a user of many of the mini.nvim modules, I tested the changes by running the fork locally.

When there was ambiguity, I took inspiration from how other themes have added support for mini.nvim and how other plugins have been supported via melange.

I appreciate this is a large PR and is difficult to test given the scope of mini.nvim, so please let me know if there is anything I can do to help with the review process!

Here are some screenshots of my nvim setup showing how mini.pick, mini.file, and mini.diff look respectively.

Closes #95.

Checklist for Plugins

Paste link to documentation listing highlight groups:

• (In colors/melange.lua) Add highlight groups
• (In README.md) Add link to plugin source repository

[savq]

Hi @tjkuson, thanks for the PR, That's a lot of highlight groups!

When the highlight group has a sensible default, I generally prefer to keep it commented out (instead of defining the link again). But otherwise the PR looks good.

I started by patching mini.pick and mini.files which are unusable on master

Yeah, that's what prompted me to open the issue 😅 I just modified MiniPickMatchCurrent in my config, but thought knew that mini needed more stuff.

[tjkuson]

When the highlight group has a sensible default, I generally prefer to keep it commented out (instead of defining the link again).

I've revisited the groups and compared them with the mini.nvim code to comment out redundant redefinitions.