feat(lua): Add a Lua module (#1815)

* feat: add lua module

* docs: add lua module

* fix: lua version test

* feat: lua module can be detected if the current dir contains a "lua" dir

* feat: enable to use luajit

* fix: improve regex

* fix based on https://github.com/starship/starship/pull/1815#discussion_r510932742

* fix based on https://github.com/starship/starship/pull/1815#discussion_r511362581

* fix based on https://github.com/starship/starship/pull/1815#discussion_r510941252

docs/config/README.md

@@ -229,6 +229,7 @@ $crystal\
 $cmd_duration\
 $custom\
 $line_break\
+$lua\
 $jobs\
 $battery\
 $time\
@@ -1494,6 +1495,44 @@ The `line_break` module separates the prompt into two lines.
 disabled = true
 ```
 
+## Lua
+
+The `lua` module shows the currently installed version of Lua.
+The module will be shown if any of the following conditions are met:
+
+- The current directory contains a `.lua-version` file
+- The current directory contains a `lua` directory
+- The current directory contains a file with the `.lua` extension
+
+### Options
+
+| Option       | Default                            | Description                                                                   |
+| ------------ | ---------------------------------- | ----------------------------------------------------------------------------- |
+| `format`     | `"via [$symbol$version]($style) "` | The format for the module.                                                    |
+| `symbol`     | `"🌙 "`                            | A format string representing the symbol of Lua.                               |
+| `style`      | `"bold blue"`                      | The style for the module.                                                     |
+| `lua_binary` | `"lua"`                            | Configures the lua binary that Starship executes when getting the version.    |
+| `disabled`   | `false`                            | Disables the `lua` module.                                                    |
+
+### Variables
+
+| Variable | Example   | Description                          |
+| -------- | --------- | ------------------------------------ |
+| version  | `v5.4.0`  | The version of `lua`                 |
+| symbol   |           | Mirrors the value of option `symbol` |
+| style\*  |           | Mirrors the value of option `style`  |
+
+\*: This variable can only be used as a part of a style string
+
+### Example
+
+```toml
+# ~/.config/starship.toml
+
+[lua]
+format = "via [🌕 $version](bold blue) "
+```
+
 ## Memory Usage
 
 The `memory_usage` module shows current system memory and swap usage.