refactor: ✨ (#418)

* refactor: ✨ move in one commit

Eveything in modules should probably be changed to `exported` defs.
The idea is to move everything first to keep proper history.

* refactor: 📝 add modules readme (wip)

* refactor: ✨ small move

* refactor: 📝 changed nestring, updated modules readme

* refactor: 📝 to document or not to document

* fix: 🐛 themes

replaced the template to use `main` and regenerated them
from lemnos themes.

* Revert "fix: 🐛 themes"

This reverts commit 4918d3633c8d2d81950a0ed0cfd9eb84241bc886.

* refactor: ✨ introduce sourced

- Created a source `root` in which sourcable demos are stored.
  Some might get converted to modules later on.
- Moved some files to bin too.

* fix: 🐛 fehbg.nu

* fix: 🐛 modules/after.nu

* moved some other stuff around

---------

Co-authored-by: Darren Schroeder <343840+fdncred@users.noreply.github.com>

modules/prompt/async_git_prompt/README.md

@@ -0,0 +1,33 @@
+This module exports commands for creating a nushell prompt that computes git status (staged and
+unstaged changes) asynchronously. This can be useful in large git repos when it is slow to obtain
+this information synchronously.
+
+To use this module:
+
+0. Place the file `async-git-prompt.nu` in the `$nu.config-path` directory (this is the directory
+   containing `init.nu` and `env.nu`).
+
+1. Use the command `async-git-prompt-string` in your own `PROMPT_COMMAND` (the file prompt.nu
+   contains an example of doing this.)
+   At this point, your prompt will be computing the information synchronously, because the cache
+   file does not yet exist.
+
+2. In a repo where git is slow, run the command `async-git-prompt-refresh-cache`.
+   Now, your prompt will be fast, but it also won't update automatically. You could investigate a good
+   way to invalidate the cache automatically, but the manual alternative is:
+
+3. Whenever you think your prompt might be stale, re-run the command `async-git-prompt-refresh-cache`.
+   Your prompt will update on one of the next times that you hit <enter>.
+
+4. It will probably be convenient to alias this, e.g.
+
+   ```nu
+   alias r = async-git-prompt-refresh-cache
+   ```
+
+5. To go back to synchronous mode, run `async-git-prompt-delete-cache`.
+
+### TODO
+
+- Automatic cache invalidation
+- Show untracked files (this can be very expensive in large repos)