Changed . token to _dot

This change allows the dotfiles to work with chezmoi (e.g: on windows)
and improves grepability with neovim/telescope

dot_config/nushell/nu_scripts/modules/prompt/powerline/README.md

@@ -0,0 +1,71 @@
+### configuration
+```
+use power.nu
+    use power_git.nu
+    power inject 0 1 {source: git,   color: '#504945'}
+    use power_kube.nu
+    power inject 1 2 {source: kube,  color: '#504945'} {
+        context: cyan
+    } {
+        reverse: true
+        separator: '@'
+    }
+    use power_utils.nu
+    power inject 0 1 {source: atuin, color: '#4C4B4A'}
+    power set time null { style: compact }
+power init
+```
+or
+```
+$env.NU_POWER_SCHEMA = [
+    [
+        {source: pwd,   color: '#353230'}
+        {source: git,   color: '#504945'}
+    ]
+    [
+        {source: proxy, color: 'dark_gray'}
+        {source: host,  color: '#353230'}
+        {source: kube,  color: '#504945'}
+        {source: time,  color: '#666560'}
+    ]
+]
+
+use power.nu
+    use power_git.nu
+    use power_kube.nu
+power init
+```
+`$env.NU_POWER_SCHEMA` support configuring dynamically
+
+## mode
+- `$env.NU_POWER_MODE = '<power|fast>'` fast mode and default mode (experimental)
+- `$env.NU_POWER_DECORATOR = '<power|plain>'` power mode and plain mode
+- `$env.NU_POWER_FRAME = '<default|fill>'` two line prompt (experimental)
+
+### benchmark
+```
+$env.NU_POWER_BENCHMARK = true
+```
+Then execute a few commands casually, such as pressing the Enter key continuously.
+then execute
+
+```
+$env.NU_POWER_MODE = 'fast' # or 'power'
+```
+
+Go ahead and press enter,
+Execute power timelog to analyze the results.
+```
+power analyze
+```
+
+## todo
+- [x] source return `null` for hiding
+- [ ] in fast mode, there is still a problem with hideable components on the left
+- [x] proxy stat invalid in plain mode
+    - '<<' not longer hide separator in `fast` mode
+- [ ] implement `power eject`
+- [ ] `$env.config.menus[].maker` can be restored
+- [x] support color theme
+- [x] refactor: theme/decorator/frame/schema
+