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/build.ps1

@@ -0,0 +1,17 @@
+try {
+  cd $PSScriptRoot/..
+
+  Remove-Item -Force -Recurse ./html | Out-Null
+  New-Item -ItemType Directory ./html | Out-Null
+  Copy-Item -Path ./css/. -Destination ./html -Recurse -Force | Out-Null
+  Copy-Item -Path ./js/. -Destination ./html -Recurse -Force | Out-Null
+
+  if ((Get-Command "lua_modules/bin/ldoc" -ErrorAction SilentlyContinue) -eq $null) {
+    echo "ldoc not found; please run docs/scripts/install.ps1"
+    exit 1
+  }
+
+  lua_modules/bin/ldoc .
+} finally {
+  popd
+}