Clean up lua docs scripts

- ldoc is now a git submodule
- ldoc can be installed using scripts/install.{sh,ps1}
- lua docs can be build using scripts/build.{sh,ps1}
- all lua docs-related files now reside inside of the docs folder

docs/scripts/serve.ps1

@@ -0,0 +1,12 @@
+try {
+  cd $PSScriptRoot/..
+
+  if ((Get-Command "python3" -ErrorAction SilentlyContinue) -eq $null) {
+    echo "python3 not found"
+    exit 1
+  }
+
+  python3 -m http.server -d html
+} finally {
+  popd
+}